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 $46.72   7.748%   $50.3399   $50.34   $50.35   $50.30  
  Purchase #2 $107.53   4.388%   $112.2484   $112.25   $112.25   $112.20  
  Purchase #3 $43.41   5.640%   $45.8583   $45.86   $45.85   $45.90  
  Purchase #4 $152.53   10.831%   $169.0505   $169.05   $169.05   $169.10  
  Purchase #5 $230.83   13.720%   $262.4999   $262.50   $262.50   $262.50  
  Purchase #6 $184.97   9.409%   $202.3738   $202.37   $202.35   $202.40  
  Purchase #7 $185.43   8.807%   $201.7608   $201.76   $201.75   $201.80  
  7 purchase totals = $951.42       $1,044.1316   $1,044.13   $1,044.10   $1,044.20