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 $57.46   3.279%   $59.3441   $59.34   $59.35   $59.30  
  Purchase #2 $155.96   8.676%   $169.4911   $169.49   $169.50   $169.50  
  Purchase #3 $121.61   3.556%   $125.9345   $125.93   $125.95   $125.90  
  Purchase #4 $245.50   13.138%   $277.7538   $277.75   $277.75   $277.80  
  Purchase #5 $12.62   10.308%   $13.9209   $13.92   $13.90   $13.90  
  Purchase #6 $114.43   8.771%   $124.4667   $124.47   $124.45   $124.50  
  Purchase #7 $22.58   7.548%   $24.2843   $24.28   $24.30   $24.30  
  7 purchase totals = $730.16       $795.1954   $795.18   $795.20   $795.20