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 $85.87   6.193%   $91.1879   $91.19   $91.20   $91.20  
  Purchase #2 $193.65   10.128%   $213.2629   $213.26   $213.25   $213.30  
  Purchase #3 $55.25   11.495%   $61.601   $61.60   $61.60   $61.60  
  Purchase #4 $169.63   6.525%   $180.6984   $180.70   $180.70   $180.70  
  Purchase #5 $146.72   8.711%   $159.5008   $159.50   $159.50   $159.50  
  Purchase #6 $6.38   5.121%   $6.7067   $6.71   $6.70   $6.70  
  Purchase #7 $166.63   9.701%   $182.7948   $182.79   $182.80   $182.80  
  7 purchase totals = $824.13       $895.7525   $895.75   $895.75   $895.80