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 $38.50   13.221%   $43.5901   $43.59   $43.60   $43.60  
  Purchase #2 $188.69   13.428%   $214.0273   $214.03   $214.05   $214.00  
  Purchase #3 $157.63   13.262%   $178.5349   $178.53   $178.55   $178.50  
  Purchase #4 $150.38   12.784%   $169.6046   $169.60   $169.60   $169.60  
  Purchase #5 $209.92   6.274%   $223.0904   $223.09   $223.10   $223.10  
  Purchase #6 $43.96   6.274%   $46.7181   $46.72   $46.70   $46.70  
  Purchase #7 $72.49   4.835%   $75.9949   $75.99   $76.00   $76.00  
  7 purchase totals = $861.57       $951.5603   $951.55   $951.60   $951.50