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 $111.41   13.314%   $126.2431   $126.24   $126.25   $126.20  
  Purchase #2 $206.93   9.214%   $225.9965   $226.00   $226.00   $226.00  
  Purchase #3 $56.83   11.328%   $63.2677   $63.27   $63.25   $63.30  
  Purchase #4 $74.70   13.198%   $84.5589   $84.56   $84.55   $84.60  
  Purchase #5 $76.91   8.312%   $83.3028   $83.30   $83.30   $83.30  
  Purchase #6 $143.93   4.276%   $150.0844   $150.08   $150.10   $150.10  
  Purchase #7 $88.64   10.274%   $97.7469   $97.75   $97.75   $97.70  
  7 purchase totals = $759.35       $831.2003   $831.20   $831.20   $831.20