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 $202.46   11.778%   $226.3057   $226.31   $226.30   $226.30  
  Purchase #2 $16.66   9.176%   $18.1887   $18.19   $18.20   $18.20  
  Purchase #3 $178.63   9.698%   $195.9535   $195.95   $195.95   $196.00  
  Purchase #4 $34.71   3.436%   $35.9026   $35.90   $35.90   $35.90  
  Purchase #5 $157.89   10.446%   $174.3832   $174.38   $174.40   $174.40  
  Purchase #6 $226.77   9.841%   $249.0864   $249.09   $249.10   $249.10  
  Purchase #7 $161.74   7.273%   $173.5034   $173.50   $173.50   $173.50  
  7 purchase totals = $978.86       $1,073.3235   $1,073.32   $1,073.35   $1,073.40