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 $202.92   9.216%   $221.6211   $221.62   $221.60   $221.60  
  Purchase #2 $201.78   5.646%   $213.1725   $213.17   $213.15   $213.20  
  Purchase #3 $193.89   4.351%   $202.3262   $202.33   $202.35   $202.30  
  Purchase #4 $122.95   11.829%   $137.4938   $137.49   $137.50   $137.50  
  Purchase #5 $181.82   8.748%   $197.7256   $197.73   $197.75   $197.70  
  Purchase #6 $159.39   11.797%   $178.1932   $178.19   $178.20   $178.20  
  Purchase #7 $105.95   8.573%   $115.0331   $115.03   $115.05   $115.00  
  7 purchase totals = $1,168.70       $1,265.5655   $1,265.56   $1,265.60   $1,265.50