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 $57.25   3.126%   $59.0396   $59.04   $59.05   $59.00  
  Purchase #2 $188.91   8.318%   $204.6235   $204.62   $204.60   $204.60  
  Purchase #3 $94.29   13.427%   $106.9503   $106.95   $106.95   $107.00  
  Purchase #4 $6.80   12.349%   $7.6397   $7.64   $7.65   $7.60  
  Purchase #5 $37.72   7.357%   $40.4951   $40.50   $40.50   $40.50  
  Purchase #6 $249.27   10.681%   $275.8945   $275.89   $275.90   $275.90  
  Purchase #7 $195.91   11.316%   $218.0792   $218.08   $218.10   $218.10  
  7 purchase totals = $830.15       $912.7219   $912.72   $912.75   $912.70