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 $235.94   7.311%   $253.1896   $253.19   $253.20   $253.20  
  Purchase #2 $64.37   13.379%   $72.9821   $72.98   $73.00   $73.00  
  Purchase #3 $109.66   13.445%   $124.4038   $124.40   $124.40   $124.40  
  Purchase #4 $59.60   8.829%   $64.8621   $64.86   $64.85   $64.90  
  Purchase #5 $164.59   10.588%   $182.0168   $182.02   $182.00   $182.00  
  Purchase #6 $176.42   10.386%   $194.743   $194.74   $194.75   $194.70  
  Purchase #7 $231.48   7.553%   $248.9637   $248.96   $248.95   $249.00  
  7 purchase totals = $1,042.06       $1,141.1611   $1,141.15   $1,141.15   $1,141.20