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 $204.93   9.229%   $223.843   $223.84   $223.85   $223.80  
  Purchase #2 $90.79   5.242%   $95.5492   $95.55   $95.55   $95.50  
  Purchase #3 $66.63   5.120%   $70.0415   $70.04   $70.05   $70.00  
  Purchase #4 $64.71   3.611%   $67.0467   $67.05   $67.05   $67.00  
  Purchase #5 $225.59   12.316%   $253.3737   $253.37   $253.35   $253.40  
  Purchase #6 $200.70   7.192%   $215.1343   $215.13   $215.15   $215.10  
  Purchase #7 $167.65   8.245%   $181.4727   $181.47   $181.45   $181.50  
  7 purchase totals = $1,021.00       $1,106.4611   $1,106.45   $1,106.45   $1,106.30