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 $194.41   6.267%   $206.5937   $206.59   $206.60   $206.60  
  Purchase #2 $228.78   11.658%   $255.4512   $255.45   $255.45   $255.50  
  Purchase #3 $29.91   13.403%   $33.9188   $33.92   $33.90   $33.90  
  Purchase #4 $77.87   8.278%   $84.3161   $84.32   $84.30   $84.30  
  Purchase #5 $61.37   5.239%   $64.5852   $64.59   $64.60   $64.60  
  Purchase #6 $17.34   8.867%   $18.8775   $18.88   $18.90   $18.90  
  Purchase #7 $229.27   6.376%   $243.8883   $243.89   $243.90   $243.90  
  7 purchase totals = $838.95       $907.6308   $907.64   $907.65   $907.70