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 $59.48   8.738%   $64.6774   $64.68   $64.70   $64.70  
  Purchase #2 $7.86   9.870%   $8.6358   $8.64   $8.65   $8.60  
  Purchase #3 $59.44   4.673%   $62.2176   $62.22   $62.20   $62.20  
  Purchase #4 $248.86   10.613%   $275.2715   $275.27   $275.25   $275.30  
  Purchase #5 $174.97   8.569%   $189.9632   $189.96   $189.95   $190.00  
  Purchase #6 $10.95   6.532%   $11.6653   $11.67   $11.65   $11.70  
  Purchase #7 $174.88   11.713%   $195.3637   $195.36   $195.35   $195.40  
  7 purchase totals = $736.44       $807.7945   $807.80   $807.75   $807.90