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 $50.50   12.393%   $56.7585   $56.76   $56.75   $56.80  
  Purchase #2 $168.64   9.404%   $184.4989   $184.50   $184.50   $184.50  
  Purchase #3 $242.29   3.208%   $250.0627   $250.06   $250.05   $250.10  
  Purchase #4 $16.93   13.819%   $19.2696   $19.27   $19.25   $19.30  
  Purchase #5 $156.68   8.195%   $169.5199   $169.52   $169.50   $169.50  
  Purchase #6 $169.53   13.504%   $192.4233   $192.42   $192.40   $192.40  
  Purchase #7 $133.56   13.453%   $151.5278   $151.53   $151.55   $151.50  
  7 purchase totals = $938.13       $1,024.0607   $1,024.06   $1,024.00   $1,024.10