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 $248.54   11.116%   $276.1677   $276.17   $276.15   $276.20  
  Purchase #2 $83.66   9.604%   $91.6947   $91.69   $91.70   $91.70  
  Purchase #3 $138.91   9.152%   $151.623   $151.62   $151.60   $151.60  
  Purchase #4 $197.92   13.242%   $224.1286   $224.13   $224.15   $224.10  
  Purchase #5 $202.37   13.783%   $230.2627   $230.26   $230.25   $230.30  
  Purchase #6 $196.38   10.667%   $217.3279   $217.33   $217.35   $217.30  
  Purchase #7 $12.62   8.265%   $13.663   $13.66   $13.65   $13.70  
  7 purchase totals = $1,080.40       $1,204.8676   $1,204.86   $1,204.85   $1,204.90