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 $22.55   13.725%   $25.645   $25.65   $25.65   $25.60  
  Purchase #2 $48.38   13.685%   $55.0008   $55.00   $55.00   $55.00  
  Purchase #3 $131.53   9.416%   $143.9149   $143.91   $143.90   $143.90  
  Purchase #4 $119.83   13.300%   $135.7674   $135.77   $135.75   $135.80  
  Purchase #5 $149.63   10.732%   $165.6883   $165.69   $165.70   $165.70  
  Purchase #6 $106.92   12.218%   $119.9835   $119.98   $120.00   $120.00  
  Purchase #7 $237.28   10.746%   $262.7781   $262.78   $262.80   $262.80  
  7 purchase totals = $816.12       $908.7780   $908.78   $908.80   $908.80