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 $91.91   12.686%   $103.5697   $103.57   $103.55   $103.60  
  Purchase #2 $204.99   13.181%   $232.0097   $232.01   $232.00   $232.00  
  Purchase #3 $124.94   13.465%   $141.7632   $141.76   $141.75   $141.80  
  Purchase #4 $10.62   3.846%   $11.0284   $11.03   $11.05   $11.00  
  Purchase #5 $68.96   5.455%   $72.7218   $72.72   $72.70   $72.70  
  Purchase #6 $149.79   6.115%   $158.9497   $158.95   $158.95   $158.90  
  Purchase #7 $17.86   9.348%   $19.5296   $19.53   $19.55   $19.50  
  7 purchase totals = $669.07       $739.5721   $739.57   $739.55   $739.50