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 $210.68   12.731%   $237.5017   $237.50   $237.50   $237.50  
  Purchase #2 $43.85   12.542%   $49.3497   $49.35   $49.35   $49.30  
  Purchase #3 $169.61   3.116%   $174.895   $174.90   $174.90   $174.90  
  Purchase #4 $244.67   6.570%   $260.7448   $260.74   $260.75   $260.70  
  Purchase #5 $26.59   13.138%   $30.0834   $30.08   $30.10   $30.10  
  Purchase #6 $248.93   7.812%   $268.3764   $268.38   $268.40   $268.40  
  Purchase #7 $96.73   5.457%   $102.0086   $102.01   $102.00   $102.00  
  7 purchase totals = $1,041.06       $1,122.9596   $1,122.96   $1,123.00   $1,122.90