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 $48.59   9.789%   $53.3465   $53.35   $53.35   $53.30  
  Purchase #2 $203.66   11.313%   $226.7001   $226.70   $226.70   $226.70  
  Purchase #3 $133.49   5.757%   $141.175   $141.18   $141.20   $141.20  
  Purchase #4 $65.67   11.561%   $73.2621   $73.26   $73.25   $73.30  
  Purchase #5 $156.77   13.211%   $177.4809   $177.48   $177.50   $177.50  
  Purchase #6 $161.42   11.445%   $179.8945   $179.89   $179.90   $179.90  
  Purchase #7 $88.49   10.369%   $97.6655   $97.67   $97.65   $97.70  
  7 purchase totals = $858.09       $949.5246   $949.53   $949.55   $949.60