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 $42.96   10.192%   $47.3385   $47.34   $47.35   $47.30  
  Purchase #2 $213.36   9.144%   $232.8696   $232.87   $232.85   $232.90  
  Purchase #3 $105.68   9.171%   $115.3719   $115.37   $115.35   $115.40  
  Purchase #4 $133.71   9.151%   $145.9458   $145.95   $145.95   $145.90  
  Purchase #5 $83.32   12.305%   $93.5725   $93.57   $93.55   $93.60  
  Purchase #6 $249.59   6.694%   $266.2976   $266.30   $266.30   $266.30  
  Purchase #7 $37.35   10.781%   $41.3767   $41.38   $41.40   $41.40  
  7 purchase totals = $865.97       $942.7726   $942.78   $942.75   $942.80