Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $186.62   6.799%   $199.3083   $199.31   $199.30   $199.30  
  Purchase #2 $98.46   11.358%   $109.6431   $109.64   $109.65   $109.60  
  Purchase #3 $175.67   13.379%   $199.1729   $199.17   $199.15   $199.20  
  Purchase #4 $215.79   13.570%   $245.0727   $245.07   $245.05   $245.10  
  Purchase #5 $136.33   13.244%   $154.3855   $154.39   $154.40   $154.40  
  Purchase #6 $211.40   12.220%   $237.2331   $237.23   $237.25   $237.20  
  Purchase #7 $162.72   11.446%   $181.3449   $181.34   $181.35   $181.30  
  7 purchase totals = $1,186.99       $1,326.1605   $1,326.15   $1,326.15   $1,326.10