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 $213.87   6.809%   $228.4324   $228.43   $228.45   $228.40  
  Purchase #2 $32.99   11.869%   $36.9056   $36.91   $36.90   $36.90  
  Purchase #3 $156.43   3.795%   $162.3665   $162.37   $162.35   $162.40  
  Purchase #4 $53.98   4.113%   $56.2002   $56.20   $56.20   $56.20  
  Purchase #5 $43.88   8.537%   $47.626   $47.63   $47.65   $47.60  
  Purchase #6 $165.93   8.816%   $180.5584   $180.56   $180.55   $180.60  
  Purchase #7 $96.28   10.858%   $106.7341   $106.73   $106.75   $106.70  
  7 purchase totals = $763.36       $818.8232   $818.83   $818.85   $818.80