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 $55.50   11.255%   $61.7465   $61.75   $61.75   $61.70  
  Purchase #2 $136.50   6.131%   $144.8688   $144.87   $144.85   $144.90  
  Purchase #3 $136.73   5.677%   $144.4922   $144.49   $144.50   $144.50  
  Purchase #4 $172.35   12.149%   $193.2888   $193.29   $193.30   $193.30  
  Purchase #5 $195.29   4.791%   $204.6463   $204.65   $204.65   $204.60  
  Purchase #6 $165.46   10.469%   $182.782   $182.78   $182.80   $182.80  
  Purchase #7 $49.38   9.513%   $54.0775   $54.08   $54.10   $54.10  
  7 purchase totals = $911.21       $985.9021   $985.91   $985.95   $985.90