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 $192.94   10.152%   $212.5273   $212.53   $212.55   $212.50  
  Purchase #2 $40.31   7.828%   $43.4655   $43.47   $43.45   $43.50  
  Purchase #3 $113.35   3.467%   $117.2798   $117.28   $117.30   $117.30  
  Purchase #4 $72.44   4.575%   $75.7541   $75.75   $75.75   $75.80  
  Purchase #5 $209.76   13.388%   $237.8427   $237.84   $237.85   $237.80  
  Purchase #6 $153.97   5.347%   $162.2028   $162.20   $162.20   $162.20  
  Purchase #7 $202.63   10.813%   $224.5404   $224.54   $224.55   $224.50  
  7 purchase totals = $985.40       $1,073.6126   $1,073.61   $1,073.65   $1,073.60