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 $245.71   3.361%   $253.9683   $253.97   $253.95   $254.00  
  Purchase #2 $208.38   13.192%   $235.8695   $235.87   $235.85   $235.90  
  Purchase #3 $45.82   10.362%   $50.5679   $50.57   $50.55   $50.60  
  Purchase #4 $23.85   10.148%   $26.2703   $26.27   $26.25   $26.30  
  Purchase #5 $58.92   13.309%   $66.7617   $66.76   $66.75   $66.80  
  Purchase #6 $100.99   8.479%   $109.5529   $109.55   $109.55   $109.60  
  Purchase #7 $152.94   12.135%   $171.4993   $171.50   $171.50   $171.50  
  7 purchase totals = $836.61       $914.4899   $914.49   $914.40   $914.70