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 $95.97   10.171%   $105.7311   $105.73   $105.75   $105.70  
  Purchase #2 $142.39   9.274%   $155.5952   $155.60   $155.60   $155.60  
  Purchase #3 $25.99   12.165%   $29.1517   $29.15   $29.15   $29.20  
  Purchase #4 $85.84   7.466%   $92.2488   $92.25   $92.25   $92.20  
  Purchase #5 $227.80   5.480%   $240.2834   $240.28   $240.30   $240.30  
  Purchase #6 $219.46   13.403%   $248.8742   $248.87   $248.85   $248.90  
  Purchase #7 $126.84   3.507%   $131.2883   $131.29   $131.30   $131.30  
  7 purchase totals = $924.29       $1,003.1727   $1,003.17   $1,003.20   $1,003.20