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 $235.86   10.367%   $260.3116   $260.31   $260.30   $260.30  
  Purchase #2 $21.25   11.741%   $23.745   $23.75   $23.75   $23.70  
  Purchase #3 $113.83   4.760%   $119.2483   $119.25   $119.25   $119.20  
  Purchase #4 $244.95   9.610%   $268.4897   $268.49   $268.50   $268.50  
  Purchase #5 $69.29   6.672%   $73.913   $73.91   $73.90   $73.90  
  Purchase #6 $121.85   6.244%   $129.4583   $129.46   $129.45   $129.50  
  Purchase #7 $92.73   5.691%   $98.0073   $98.01   $98.00   $98.00  
  7 purchase totals = $899.76       $973.1732   $973.18   $973.15   $973.10