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 $24.72   7.681%   $26.6187   $26.62   $26.60   $26.60  
  Purchase #2 $133.34   4.761%   $139.6883   $139.69   $139.70   $139.70  
  Purchase #3 $137.58   4.791%   $144.1715   $144.17   $144.15   $144.20  
  Purchase #4 $181.68   6.714%   $193.878   $193.88   $193.90   $193.90  
  Purchase #5 $189.31   3.346%   $195.6443   $195.64   $195.65   $195.60  
  Purchase #6 $11.26   7.219%   $12.0729   $12.07   $12.05   $12.10  
  Purchase #7 $101.86   8.115%   $110.1259   $110.13   $110.15   $110.10  
  7 purchase totals = $779.75       $822.1996   $822.20   $822.20   $822.20