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 $173.75   9.566%   $190.3709   $190.37   $190.35   $190.40  
  Purchase #2 $241.25   10.468%   $266.5041   $266.50   $266.50   $266.50  
  Purchase #3 $170.83   9.104%   $186.3824   $186.38   $186.40   $186.40  
  Purchase #4 $93.47   4.827%   $97.9818   $97.98   $98.00   $98.00  
  Purchase #5 $117.46   12.189%   $131.7772   $131.78   $131.80   $131.80  
  Purchase #6 $237.27   9.250%   $259.2175   $259.22   $259.20   $259.20  
  Purchase #7 $185.27   4.764%   $194.0963   $194.10   $194.10   $194.10  
  7 purchase totals = $1,219.30       $1,326.3302   $1,326.33   $1,326.35   $1,326.40