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 $51.99   5.682%   $54.9441   $54.94   $54.95   $54.90  
  Purchase #2 $106.33   5.768%   $112.4631   $112.46   $112.45   $112.50  
  Purchase #3 $52.82   6.430%   $56.2163   $56.22   $56.20   $56.20  
  Purchase #4 $59.93   8.503%   $65.0258   $65.03   $65.05   $65.00  
  Purchase #5 $192.98   11.139%   $214.476   $214.48   $214.50   $214.50  
  Purchase #6 $207.49   5.281%   $218.4475   $218.45   $218.45   $218.40  
  Purchase #7 $47.89   3.142%   $49.3947   $49.39   $49.40   $49.40  
  7 purchase totals = $719.43       $770.9675   $770.97   $771.00   $770.90