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 $117.26   12.197%   $131.5622   $131.56   $131.55   $131.60  
  Purchase #2 $133.71   9.268%   $146.1022   $146.10   $146.10   $146.10  
  Purchase #3 $48.36   3.309%   $49.9602   $49.96   $49.95   $50.00  
  Purchase #4 $206.89   9.520%   $226.5859   $226.59   $226.60   $226.60  
  Purchase #5 $121.92   11.173%   $135.5421   $135.54   $135.55   $135.50  
  Purchase #6 $34.75   13.412%   $39.4107   $39.41   $39.40   $39.40  
  Purchase #7 $45.29   3.211%   $46.7443   $46.74   $46.75   $46.70  
  7 purchase totals = $708.18       $775.9076   $775.90   $775.90   $775.90