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 $32.60   6.135%   $34.6   $34.60   $34.60   $34.60  
  Purchase #2 $179.52   12.202%   $201.425   $201.43   $201.45   $201.40  
  Purchase #3 $130.35   13.183%   $147.534   $147.53   $147.55   $147.50  
  Purchase #4 $237.73   3.422%   $245.8651   $245.87   $245.85   $245.90  
  Purchase #5 $23.45   8.690%   $25.4878   $25.49   $25.50   $25.50  
  Purchase #6 $180.60   9.133%   $197.0942   $197.09   $197.10   $197.10  
  Purchase #7 $94.33   3.559%   $97.6872   $97.69   $97.70   $97.70  
  7 purchase totals = $878.58       $949.6933   $949.70   $949.75   $949.70