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 $68.72   9.627%   $75.3357   $75.34   $75.35   $75.30  
  Purchase #2 $42.57   4.319%   $44.4086   $44.41   $44.40   $44.40  
  Purchase #3 $183.84   11.395%   $204.7886   $204.79   $204.80   $204.80  
  Purchase #4 $59.66   11.704%   $66.6426   $66.64   $66.65   $66.60  
  Purchase #5 $9.86   9.211%   $10.7682   $10.77   $10.75   $10.80  
  Purchase #6 $173.83   6.554%   $185.2228   $185.22   $185.20   $185.20  
  Purchase #7 $35.52   5.649%   $37.5265   $37.53   $37.55   $37.50  
  7 purchase totals = $574.00       $624.6930   $624.70   $624.70   $624.60