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 $24.54   7.359%   $26.3459   $26.35   $26.35   $26.30  
  Purchase #2 $245.33   9.510%   $268.6609   $268.66   $268.65   $268.70  
  Purchase #3 $93.88   10.376%   $103.621   $103.62   $103.60   $103.60  
  Purchase #4 $44.55   9.675%   $48.8602   $48.86   $48.85   $48.90  
  Purchase #5 $35.28   13.399%   $40.0072   $40.01   $40.00   $40.00  
  Purchase #6 $232.32   12.102%   $260.4354   $260.44   $260.45   $260.40  
  Purchase #7 $33.78   11.309%   $37.6002   $37.60   $37.60   $37.60  
  7 purchase totals = $709.68       $785.5308   $785.54   $785.50   $785.50