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 $169.49   9.313%   $185.2746   $185.27   $185.25   $185.30  
  Purchase #2 $34.44   5.584%   $36.3631   $36.36   $36.35   $36.40  
  Purchase #3 $175.38   4.673%   $183.5755   $183.58   $183.60   $183.60  
  Purchase #4 $81.49   5.444%   $85.9263   $85.93   $85.95   $85.90  
  Purchase #5 $191.69   11.372%   $213.489   $213.49   $213.50   $213.50  
  Purchase #6 $140.63   12.757%   $158.5702   $158.57   $158.55   $158.60  
  Purchase #7 $149.95   7.700%   $161.4962   $161.50   $161.50   $161.50  
  7 purchase totals = $943.07       $1,024.6949   $1,024.70   $1,024.70   $1,024.80