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 $233.25   9.571%   $255.5744   $255.57   $255.55   $255.60  
  Purchase #2 $247.71   6.157%   $262.9615   $262.96   $262.95   $263.00  
  Purchase #3 $165.38   13.225%   $187.2515   $187.25   $187.25   $187.30  
  Purchase #4 $228.46   7.187%   $244.8794   $244.88   $244.90   $244.90  
  Purchase #5 $226.63   12.233%   $254.3536   $254.35   $254.35   $254.40  
  Purchase #6 $240.45   7.222%   $257.8153   $257.82   $257.80   $257.80  
  Purchase #7 $78.52   5.753%   $83.0373   $83.04   $83.05   $83.00  
  7 purchase totals = $1,420.40       $1,545.8730   $1,545.87   $1,545.85   $1,546.00