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 $62.29   5.359%   $65.6281   $65.63   $65.65   $65.60  
  Purchase #2 $184.99   10.507%   $204.4269   $204.43   $204.45   $204.40  
  Purchase #3 $33.32   8.152%   $36.0362   $36.04   $36.05   $36.00  
  Purchase #4 $158.72   4.836%   $166.3957   $166.40   $166.40   $166.40  
  Purchase #5 $23.64   10.587%   $26.1428   $26.14   $26.15   $26.10  
  Purchase #6 $84.83   3.810%   $88.062   $88.06   $88.05   $88.10  
  Purchase #7 $182.59   7.176%   $195.6927   $195.69   $195.70   $195.70  
  7 purchase totals = $730.38       $782.3844   $782.39   $782.45   $782.30