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 $224.53   12.692%   $253.0273   $253.03   $253.05   $253.00  
  Purchase #2 $22.59   12.112%   $25.3261   $25.33   $25.35   $25.30  
  Purchase #3 $167.89   3.808%   $174.2833   $174.28   $174.30   $174.30  
  Purchase #4 $24.96   7.502%   $26.8325   $26.83   $26.85   $26.80  
  Purchase #5 $122.37   6.512%   $130.3387   $130.34   $130.35   $130.30  
  Purchase #6 $184.66   7.735%   $198.9435   $198.94   $198.95   $198.90  
  Purchase #7 $64.97   5.655%   $68.6441   $68.64   $68.65   $68.60  
  7 purchase totals = $811.97       $877.3955   $877.39   $877.50   $877.20