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 $113.88   4.800%   $119.3462   $119.35   $119.35   $119.30  
  Purchase #2 $107.25   11.304%   $119.3735   $119.37   $119.35   $119.40  
  Purchase #3 $90.28   5.690%   $95.4169   $95.42   $95.40   $95.40  
  Purchase #4 $246.70   4.399%   $257.5523   $257.55   $257.55   $257.60  
  Purchase #5 $23.92   8.403%   $25.93   $25.93   $25.95   $25.90  
  Purchase #6 $88.34   3.722%   $91.628   $91.63   $91.65   $91.60  
  Purchase #7 $188.98   4.211%   $196.9379   $196.94   $196.95   $196.90  
  7 purchase totals = $859.35       $906.1848   $906.19   $906.20   $906.10