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 $232.43   7.752%   $250.448   $250.45   $250.45   $250.40  
  Purchase #2 $86.71   8.615%   $94.1801   $94.18   $94.20   $94.20  
  Purchase #3 $74.94   7.471%   $80.5388   $80.54   $80.55   $80.50  
  Purchase #4 $178.94   4.143%   $186.3535   $186.35   $186.35   $186.40  
  Purchase #5 $161.78   8.550%   $175.6122   $175.61   $175.60   $175.60  
  Purchase #6 $182.85   6.367%   $194.4921   $194.49   $194.50   $194.50  
  Purchase #7 $10.54   3.760%   $10.9363   $10.94   $10.95   $10.90  
  7 purchase totals = $928.19       $992.5610   $992.56   $992.60   $992.50