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 $46.39   6.761%   $49.5264   $49.53   $49.55   $49.50  
  Purchase #2 $185.89   9.764%   $204.0403   $204.04   $204.05   $204.00  
  Purchase #3 $238.81   5.205%   $251.2401   $251.24   $251.25   $251.20  
  Purchase #4 $82.65   13.129%   $93.5011   $93.50   $93.50   $93.50  
  Purchase #5 $49.55   4.862%   $51.9591   $51.96   $51.95   $52.00  
  Purchase #6 $159.92   11.152%   $177.7543   $177.75   $177.75   $177.80  
  Purchase #7 $19.31   4.597%   $20.1977   $20.20   $20.20   $20.20  
  7 purchase totals = $782.52       $848.2190   $848.22   $848.25   $848.20