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 $77.37   6.467%   $82.3735   $82.37   $82.35   $82.40  
  Purchase #2 $84.87   10.668%   $93.9239   $93.92   $93.90   $93.90  
  Purchase #3 $243.78   12.477%   $274.1964   $274.20   $274.20   $274.20  
  Purchase #4 $184.95   6.129%   $196.2856   $196.29   $196.30   $196.30  
  Purchase #5 $104.40   13.218%   $118.1996   $118.20   $118.20   $118.20  
  Purchase #6 $161.59   9.456%   $176.87   $176.87   $176.85   $176.90  
  Purchase #7 $52.97   3.852%   $55.0104   $55.01   $55.00   $55.00  
  7 purchase totals = $909.93       $996.8594   $996.86   $996.80   $996.90