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 $42.77   11.669%   $47.7608   $47.76   $47.75   $47.80  
  Purchase #2 $198.54   4.200%   $206.8787   $206.88   $206.90   $206.90  
  Purchase #3 $41.60   13.430%   $47.1869   $47.19   $47.20   $47.20  
  Purchase #4 $240.47   8.226%   $260.2511   $260.25   $260.25   $260.30  
  Purchase #5 $110.65   5.188%   $116.3905   $116.39   $116.40   $116.40  
  Purchase #6 $180.54   12.365%   $202.8638   $202.86   $202.85   $202.90  
  Purchase #7 $44.51   11.521%   $49.638   $49.64   $49.65   $49.60  
  7 purchase totals = $859.08       $930.9698   $930.97   $931.00   $931.10