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 $100.41   6.334%   $106.77   $106.77   $106.75   $106.80  
  Purchase #2 $199.72   8.792%   $217.2794   $217.28   $217.30   $217.30  
  Purchase #3 $232.45   5.496%   $245.2255   $245.23   $245.25   $245.20  
  Purchase #4 $136.67   9.493%   $149.6441   $149.64   $149.65   $149.60  
  Purchase #5 $99.31   6.746%   $106.0095   $106.01   $106.00   $106.00  
  Purchase #6 $199.59   12.816%   $225.1695   $225.17   $225.15   $225.20  
  Purchase #7 $36.28   8.572%   $39.3899   $39.39   $39.40   $39.40  
  7 purchase totals = $1,004.43       $1,089.4879   $1,089.49   $1,089.50   $1,089.50