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 $89.87   9.395%   $98.3133   $98.31   $98.30   $98.30  
  Purchase #2 $81.52   5.422%   $85.94   $85.94   $85.95   $85.90  
  Purchase #3 $141.32   4.545%   $147.743   $147.74   $147.75   $147.70  
  Purchase #4 $205.69   9.209%   $224.632   $224.63   $224.65   $224.60  
  Purchase #5 $194.76   10.563%   $215.3325   $215.33   $215.35   $215.30  
  Purchase #6 $195.67   8.142%   $211.6015   $211.60   $211.60   $211.60  
  Purchase #7 $242.64   4.690%   $254.0198   $254.02   $254.00   $254.00  
  7 purchase totals = $1,151.47       $1,237.5821   $1,237.57   $1,237.60   $1,237.40