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 $58.36   3.169%   $60.2094   $60.21   $60.20   $60.20  
  Purchase #2 $73.84   12.429%   $83.0176   $83.02   $83.00   $83.00  
  Purchase #3 $163.54   12.825%   $184.514   $184.51   $184.50   $184.50  
  Purchase #4 $80.72   3.148%   $83.2611   $83.26   $83.25   $83.30  
  Purchase #5 $170.81   10.483%   $188.716   $188.72   $188.70   $188.70  
  Purchase #6 $235.91   9.541%   $258.4182   $258.42   $258.40   $258.40  
  Purchase #7 $68.56   12.333%   $77.0155   $77.02   $77.00   $77.00  
  7 purchase totals = $851.74       $935.1518   $935.16   $935.05   $935.10