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 $56.78   6.576%   $60.5139   $60.51   $60.50   $60.50  
  Purchase #2 $133.88   11.502%   $149.2789   $149.28   $149.30   $149.30  
  Purchase #3 $17.76   7.262%   $19.0497   $19.05   $19.05   $19.00  
  Purchase #4 $41.61   13.732%   $47.3239   $47.32   $47.30   $47.30  
  Purchase #5 $186.53   9.529%   $204.3044   $204.30   $204.30   $204.30  
  Purchase #6 $136.99   6.423%   $145.7889   $145.79   $145.80   $145.80  
  Purchase #7 $122.48   3.259%   $126.4716   $126.47   $126.45   $126.50  
  7 purchase totals = $696.03       $752.7313   $752.72   $752.70   $752.70