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 $184.96   5.308%   $194.7777   $194.78   $194.80   $194.80  
  Purchase #2 $58.76   3.641%   $60.8995   $60.90   $60.90   $60.90  
  Purchase #3 $180.37   13.211%   $204.1987   $204.20   $204.20   $204.20  
  Purchase #4 $159.53   11.112%   $177.257   $177.26   $177.25   $177.30  
  Purchase #5 $212.75   5.578%   $224.6172   $224.62   $224.60   $224.60  
  Purchase #6 $198.76   7.791%   $214.2454   $214.25   $214.25   $214.20  
  Purchase #7 $132.81   3.744%   $137.7824   $137.78   $137.80   $137.80  
  7 purchase totals = $1,127.94       $1,213.7779   $1,213.79   $1,213.80   $1,213.80