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 $57.49   4.292%   $59.9575   $59.96   $59.95   $60.00  
  Purchase #2 $182.90   7.818%   $197.1991   $197.20   $197.20   $197.20  
  Purchase #3 $107.58   9.754%   $118.0734   $118.07   $118.05   $118.10  
  Purchase #4 $157.29   6.105%   $166.8926   $166.89   $166.90   $166.90  
  Purchase #5 $156.81   11.721%   $175.1897   $175.19   $175.20   $175.20  
  Purchase #6 $108.40   12.188%   $121.6118   $121.61   $121.60   $121.60  
  Purchase #7 $235.72   11.217%   $262.1607   $262.16   $262.15   $262.20  
  7 purchase totals = $1,006.19       $1,101.0848   $1,101.08   $1,101.05   $1,101.20