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 $84.47   10.690%   $93.4998   $93.50   $93.50   $93.50  
  Purchase #2 $68.94   8.112%   $74.5324   $74.53   $74.55   $74.50  
  Purchase #3 $212.40   12.756%   $239.4937   $239.49   $239.50   $239.50  
  Purchase #4 $67.43   5.146%   $70.8999   $70.90   $70.90   $70.90  
  Purchase #5 $149.36   11.808%   $166.9964   $167.00   $167.00   $167.00  
  Purchase #6 $94.57   3.219%   $97.6142   $97.61   $97.60   $97.60  
  Purchase #7 $124.48   4.519%   $130.1053   $130.11   $130.10   $130.10  
  7 purchase totals = $801.65       $873.1417   $873.14   $873.15   $873.10