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 $24.91   3.747%   $25.8434   $25.84   $25.85   $25.80  
  Purchase #2 $207.55   6.413%   $220.8602   $220.86   $220.85   $220.90  
  Purchase #3 $173.73   4.641%   $181.7928   $181.79   $181.80   $181.80  
  Purchase #4 $103.96   10.347%   $114.7167   $114.72   $114.70   $114.70  
  Purchase #5 $153.32   6.176%   $162.789   $162.79   $162.80   $162.80  
  Purchase #6 $72.81   5.309%   $76.6755   $76.68   $76.70   $76.70  
  Purchase #7 $229.55   5.370%   $241.8768   $241.88   $241.90   $241.90  
  7 purchase totals = $965.83       $1,024.5544   $1,024.56   $1,024.60   $1,024.60