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 $186.43   3.195%   $192.3864   $192.39   $192.40   $192.40  
  Purchase #2 $197.37   3.138%   $203.5635   $203.56   $203.55   $203.60  
  Purchase #3 $245.29   9.554%   $268.725   $268.73   $268.75   $268.70  
  Purchase #4 $58.48   5.749%   $61.842   $61.84   $61.85   $61.80  
  Purchase #5 $59.82   3.794%   $62.0896   $62.09   $62.10   $62.10  
  Purchase #6 $35.32   7.385%   $37.9284   $37.93   $37.95   $37.90  
  Purchase #7 $133.71   3.621%   $138.5516   $138.55   $138.55   $138.60  
  7 purchase totals = $916.42       $965.0865   $965.09   $965.15   $965.10