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 $85.60   10.252%   $94.3757   $94.38   $94.40   $94.40  
  Purchase #2 $235.44   13.760%   $267.8365   $267.84   $267.85   $267.80  
  Purchase #3 $48.38   7.267%   $51.8958   $51.90   $51.90   $51.90  
  Purchase #4 $183.58   4.452%   $191.753   $191.75   $191.75   $191.80  
  Purchase #5 $176.26   5.768%   $186.4267   $186.43   $186.45   $186.40  
  Purchase #6 $245.66   12.139%   $275.4807   $275.48   $275.50   $275.50  
  Purchase #7 $11.83   11.394%   $13.1779   $13.18   $13.20   $13.20  
  7 purchase totals = $986.75       $1,080.9463   $1,080.96   $1,081.05   $1,081.00