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 $210.81   10.457%   $232.8544   $232.85   $232.85   $232.90  
  Purchase #2 $166.54   4.577%   $174.1625   $174.16   $174.15   $174.20  
  Purchase #3 $83.94   12.298%   $94.2629   $94.26   $94.25   $94.30  
  Purchase #4 $8.80   5.201%   $9.2577   $9.26   $9.25   $9.30  
  Purchase #5 $239.93   4.195%   $249.9951   $250.00   $250.00   $250.00  
  Purchase #6 $178.64   11.116%   $198.4976   $198.50   $198.50   $198.50  
  Purchase #7 $73.88   5.683%   $78.0786   $78.08   $78.10   $78.10  
  7 purchase totals = $962.54       $1,037.1088   $1,037.11   $1,037.10   $1,037.30