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 $173.52   13.863%   $197.5751   $197.58   $197.60   $197.60  
  Purchase #2 $196.95   11.846%   $220.2807   $220.28   $220.30   $220.30  
  Purchase #3 $116.70   6.800%   $124.6356   $124.64   $124.65   $124.60  
  Purchase #4 $237.27   9.148%   $258.9755   $258.98   $259.00   $259.00  
  Purchase #5 $241.92   7.763%   $260.7002   $260.70   $260.70   $260.70  
  Purchase #6 $69.79   10.764%   $77.3022   $77.30   $77.30   $77.30  
  Purchase #7 $194.98   9.382%   $213.273   $213.27   $213.25   $213.30  
  7 purchase totals = $1,231.13       $1,352.7423   $1,352.75   $1,352.80   $1,352.80