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 $241.82   9.203%   $264.0747   $264.07   $264.05   $264.10  
  Purchase #2 $137.36   7.283%   $147.3639   $147.36   $147.35   $147.40  
  Purchase #3 $59.44   7.270%   $63.7613   $63.76   $63.75   $63.80  
  Purchase #4 $141.87   11.491%   $158.1723   $158.17   $158.15   $158.20  
  Purchase #5 $91.88   11.435%   $102.3865   $102.39   $102.40   $102.40  
  Purchase #6 $155.91   13.550%   $177.0358   $177.04   $177.05   $177.00  
  Purchase #7 $25.92   9.655%   $28.4226   $28.42   $28.40   $28.40  
  7 purchase totals = $854.20       $941.2171   $941.21   $941.15   $941.30