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 $46.80   13.335%   $53.0408   $53.04   $53.05   $53.00  
  Purchase #2 $209.84   13.474%   $238.1138   $238.11   $238.10   $238.10  
  Purchase #3 $16.92   13.210%   $19.1551   $19.16   $19.15   $19.20  
  Purchase #4 $226.97   8.629%   $246.5552   $246.56   $246.55   $246.60  
  Purchase #5 $66.34   11.539%   $73.995   $74.00   $74.00   $74.00  
  Purchase #6 $102.75   10.558%   $113.5983   $113.60   $113.60   $113.60  
  Purchase #7 $121.78   7.673%   $131.1242   $131.12   $131.10   $131.10  
  7 purchase totals = $791.40       $875.5824   $875.59   $875.55   $875.60