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 $96.89   8.344%   $104.9745   $104.97   $104.95   $105.00  
  Purchase #2 $202.55   11.347%   $225.5333   $225.53   $225.55   $225.50  
  Purchase #3 $248.92   3.610%   $257.906   $257.91   $257.90   $257.90  
  Purchase #4 $118.86   12.374%   $133.5677   $133.57   $133.55   $133.60  
  Purchase #5 $246.89   6.190%   $262.1725   $262.17   $262.15   $262.20  
  Purchase #6 $102.78   11.458%   $114.5565   $114.56   $114.55   $114.60  
  Purchase #7 $176.79   3.776%   $183.4656   $183.47   $183.45   $183.50  
  7 purchase totals = $1,193.68       $1,282.1761   $1,282.18   $1,282.10   $1,282.30