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 $96.84   4.572%   $101.2675   $101.27   $101.25   $101.30  
  Purchase #2 $166.53   9.569%   $182.4653   $182.47   $182.45   $182.50  
  Purchase #3 $54.52   5.334%   $57.4281   $57.43   $57.45   $57.40  
  Purchase #4 $21.55   9.309%   $23.5561   $23.56   $23.55   $23.60  
  Purchase #5 $249.82   9.651%   $273.9301   $273.93   $273.95   $273.90  
  Purchase #6 $145.37   6.293%   $154.5181   $154.52   $154.50   $154.50  
  Purchase #7 $219.31   7.361%   $235.4534   $235.45   $235.45   $235.50  
  7 purchase totals = $953.94       $1,028.6186   $1,028.63   $1,028.60   $1,028.70