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 $59.42   3.468%   $61.4807   $61.48   $61.50   $61.50  
  Purchase #2 $177.44   3.216%   $183.1465   $183.15   $183.15   $183.10  
  Purchase #3 $22.33   8.777%   $24.2899   $24.29   $24.30   $24.30  
  Purchase #4 $152.44   3.504%   $157.7815   $157.78   $157.80   $157.80  
  Purchase #5 $187.53   7.419%   $201.4429   $201.44   $201.45   $201.40  
  Purchase #6 $24.26   5.688%   $25.6399   $25.64   $25.65   $25.60  
  Purchase #7 $145.57   10.517%   $160.8796   $160.88   $160.90   $160.90  
  7 purchase totals = $768.99       $814.6610   $814.66   $814.75   $814.60