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 $67.34   12.504%   $75.7602   $75.76   $75.75   $75.80  
  Purchase #2 $62.63   13.303%   $70.9617   $70.96   $70.95   $71.00  
  Purchase #3 $10.89   4.782%   $11.4108   $11.41   $11.40   $11.40  
  Purchase #4 $184.45   6.567%   $196.5628   $196.56   $196.55   $196.60  
  Purchase #5 $139.80   10.499%   $154.4776   $154.48   $154.50   $154.50  
  Purchase #6 $214.99   4.245%   $224.1163   $224.12   $224.10   $224.10  
  Purchase #7 $109.53   11.652%   $122.2924   $122.29   $122.30   $122.30  
  7 purchase totals = $789.63       $855.5818   $855.58   $855.55   $855.70