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 $243.61   11.503%   $271.6325   $271.63   $271.65   $271.60  
  Purchase #2 $195.67   3.390%   $202.3032   $202.30   $202.30   $202.30  
  Purchase #3 $217.64   3.531%   $225.3249   $225.32   $225.30   $225.30  
  Purchase #4 $84.78   3.701%   $87.9177   $87.92   $87.90   $87.90  
  Purchase #5 $139.92   11.411%   $155.8863   $155.89   $155.90   $155.90  
  Purchase #6 $227.62   11.273%   $253.2796   $253.28   $253.30   $253.30  
  Purchase #7 $185.89   8.751%   $202.1572   $202.16   $202.15   $202.20  
  7 purchase totals = $1,295.13       $1,398.5014   $1,398.50   $1,398.50   $1,398.50