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 $180.36   7.603%   $194.0728   $194.07   $194.05   $194.10  
  Purchase #2 $111.99   12.222%   $125.6774   $125.68   $125.70   $125.70  
  Purchase #3 $25.51   4.403%   $26.6332   $26.63   $26.65   $26.60  
  Purchase #4 $82.90   10.230%   $91.3807   $91.38   $91.40   $91.40  
  Purchase #5 $47.43   8.424%   $51.4255   $51.43   $51.45   $51.40  
  Purchase #6 $113.41   8.794%   $123.3833   $123.38   $123.40   $123.40  
  Purchase #7 $204.97   7.151%   $219.6274   $219.63   $219.65   $219.60  
  7 purchase totals = $766.57       $832.2003   $832.20   $832.30   $832.20