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 $241.33   10.869%   $267.5602   $267.56   $267.55   $267.60  
  Purchase #2 $106.66   7.168%   $114.3054   $114.31   $114.30   $114.30  
  Purchase #3 $123.65   8.646%   $134.3408   $134.34   $134.35   $134.30  
  Purchase #4 $19.39   8.198%   $20.9796   $20.98   $21.00   $21.00  
  Purchase #5 $151.63   5.867%   $160.5261   $160.53   $160.55   $160.50  
  Purchase #6 $233.53   5.237%   $245.76   $245.76   $245.75   $245.80  
  Purchase #7 $169.55   3.563%   $175.5911   $175.59   $175.60   $175.60  
  7 purchase totals = $1,045.74       $1,119.0632   $1,119.07   $1,119.10   $1,119.10