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 $60.31   6.357%   $64.1439   $64.14   $64.15   $64.10  
  Purchase #2 $44.45   3.573%   $46.0382   $46.04   $46.05   $46.00  
  Purchase #3 $223.38   7.573%   $240.2966   $240.30   $240.30   $240.30  
  Purchase #4 $65.29   7.797%   $70.3807   $70.38   $70.40   $70.40  
  Purchase #5 $176.52   13.364%   $200.1101   $200.11   $200.10   $200.10  
  Purchase #6 $167.65   3.630%   $173.7357   $173.74   $173.75   $173.70  
  Purchase #7 $154.67   12.321%   $173.7269   $173.73   $173.75   $173.70  
  7 purchase totals = $892.27       $968.4321   $968.44   $968.50   $968.30