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 $28.44   13.571%   $32.2996   $32.30   $32.30   $32.30  
  Purchase #2 $45.88   9.427%   $50.2051   $50.21   $50.20   $50.20  
  Purchase #3 $244.70   5.821%   $258.944   $258.94   $258.95   $258.90  
  Purchase #4 $212.51   4.699%   $222.4958   $222.50   $222.50   $222.50  
  Purchase #5 $62.43   13.555%   $70.8924   $70.89   $70.90   $70.90  
  Purchase #6 $195.49   8.675%   $212.4488   $212.45   $212.45   $212.40  
  Purchase #7 $205.65   3.252%   $212.3377   $212.34   $212.35   $212.30  
  7 purchase totals = $995.10       $1,059.6234   $1,059.63   $1,059.65   $1,059.50