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 $247.57   7.303%   $265.65   $265.65   $265.65   $265.70  
  Purchase #2 $166.46   13.699%   $189.2634   $189.26   $189.25   $189.30  
  Purchase #3 $60.40   3.246%   $62.3606   $62.36   $62.35   $62.40  
  Purchase #4 $36.56   11.398%   $40.7271   $40.73   $40.75   $40.70  
  Purchase #5 $129.89   4.613%   $135.8818   $135.88   $135.90   $135.90  
  Purchase #6 $38.90   8.361%   $42.1524   $42.15   $42.15   $42.20  
  Purchase #7 $216.89   10.533%   $239.735   $239.74   $239.75   $239.70  
  7 purchase totals = $896.67       $975.7703   $975.77   $975.80   $975.90