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 $49.72   6.548%   $52.9757   $52.98   $53.00   $53.00  
  Purchase #2 $191.44   13.837%   $217.9296   $217.93   $217.95   $217.90  
  Purchase #3 $15.99   13.208%   $18.102   $18.10   $18.10   $18.10  
  Purchase #4 $74.55   4.532%   $77.9286   $77.93   $77.95   $77.90  
  Purchase #5 $184.44   12.482%   $207.4618   $207.46   $207.45   $207.50  
  Purchase #6 $37.49   8.275%   $40.5923   $40.59   $40.60   $40.60  
  Purchase #7 $156.85   9.584%   $171.8825   $171.88   $171.90   $171.90  
  7 purchase totals = $710.48       $786.8725   $786.87   $786.95   $786.90