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 $82.90   13.188%   $93.8329   $93.83   $93.85   $93.80  
  Purchase #2 $232.82   6.508%   $247.9719   $247.97   $247.95   $248.00  
  Purchase #3 $221.99   11.673%   $247.9029   $247.90   $247.90   $247.90  
  Purchase #4 $146.97   10.781%   $162.8148   $162.81   $162.80   $162.80  
  Purchase #5 $236.26   13.256%   $267.5786   $267.58   $267.60   $267.60  
  Purchase #6 $104.73   13.533%   $118.9031   $118.90   $118.90   $118.90  
  Purchase #7 $159.80   11.149%   $177.6161   $177.62   $177.60   $177.60  
  7 purchase totals = $1,185.47       $1,316.6203   $1,316.61   $1,316.60   $1,316.60