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 $204.29   9.303%   $223.2951   $223.30   $223.30   $223.30  
  Purchase #2 $167.27   11.392%   $186.3254   $186.33   $186.35   $186.30  
  Purchase #3 $123.38   5.706%   $130.4201   $130.42   $130.40   $130.40  
  Purchase #4 $194.97   4.410%   $203.5682   $203.57   $203.55   $203.60  
  Purchase #5 $53.36   12.282%   $59.9137   $59.91   $59.90   $59.90  
  Purchase #6 $199.63   12.641%   $224.8652   $224.87   $224.85   $224.90  
  Purchase #7 $173.74   3.677%   $180.1284   $180.13   $180.15   $180.10  
  7 purchase totals = $1,116.64       $1,208.5161   $1,208.53   $1,208.50   $1,208.50