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 $242.62   13.353%   $275.017   $275.02   $275.00   $275.00  
  Purchase #2 $117.81   11.492%   $131.3487   $131.35   $131.35   $131.30  
  Purchase #3 $40.96   9.286%   $44.7635   $44.76   $44.75   $44.80  
  Purchase #4 $100.52   12.471%   $113.0558   $113.06   $113.05   $113.10  
  Purchase #5 $109.52   4.171%   $114.0881   $114.09   $114.10   $114.10  
  Purchase #6 $102.70   5.609%   $108.4604   $108.46   $108.45   $108.50  
  Purchase #7 $230.91   8.160%   $249.7523   $249.75   $249.75   $249.80  
  7 purchase totals = $945.04       $1,036.4858   $1,036.49   $1,036.45   $1,036.60