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 $178.51   9.236%   $194.9972   $195.00   $195.00   $195.00  
  Purchase #2 $46.32   6.489%   $49.3257   $49.33   $49.35   $49.30  
  Purchase #3 $221.30   10.237%   $243.9545   $243.95   $243.95   $244.00  
  Purchase #4 $20.36   6.254%   $21.6333   $21.63   $21.65   $21.60  
  Purchase #5 $51.93   10.392%   $57.3266   $57.33   $57.35   $57.30  
  Purchase #6 $44.95   8.129%   $48.604   $48.60   $48.60   $48.60  
  Purchase #7 $168.77   9.670%   $185.0901   $185.09   $185.10   $185.10  
  7 purchase totals = $732.14       $800.9314   $800.93   $801.00   $800.90