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 $84.98   13.360%   $96.3333   $96.33   $96.35   $96.30  
  Purchase #2 $220.31   7.373%   $236.5535   $236.55   $236.55   $236.60  
  Purchase #3 $57.73   5.587%   $60.9554   $60.96   $60.95   $61.00  
  Purchase #4 $73.47   7.289%   $78.8252   $78.83   $78.85   $78.80  
  Purchase #5 $206.91   5.342%   $217.9631   $217.96   $217.95   $218.00  
  Purchase #6 $81.60   4.122%   $84.9636   $84.96   $84.95   $85.00  
  Purchase #7 $222.66   11.823%   $248.9851   $248.99   $249.00   $249.00  
  7 purchase totals = $947.66       $1,024.5792   $1,024.58   $1,024.60   $1,024.70