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 $46.98   7.749%   $50.6205   $50.62   $50.60   $50.60  
  Purchase #2 $131.80   9.597%   $144.4488   $144.45   $144.45   $144.40  
  Purchase #3 $218.29   12.637%   $245.8753   $245.88   $245.90   $245.90  
  Purchase #4 $112.35   9.153%   $122.6334   $122.63   $122.65   $122.60  
  Purchase #5 $14.92   10.144%   $16.4335   $16.43   $16.45   $16.40  
  Purchase #6 $186.76   9.485%   $204.4742   $204.47   $204.45   $204.50  
  Purchase #7 $234.55   6.569%   $249.9576   $249.96   $249.95   $250.00  
  7 purchase totals = $945.65       $1,034.4433   $1,034.44   $1,034.45   $1,034.40