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 $248.60   6.323%   $264.319   $264.32   $264.30   $264.30  
  Purchase #2 $13.62   4.854%   $14.2811   $14.28   $14.30   $14.30  
  Purchase #3 $93.32   8.524%   $101.2746   $101.27   $101.25   $101.30  
  Purchase #4 $240.34   8.495%   $260.7569   $260.76   $260.75   $260.80  
  Purchase #5 $222.29   10.696%   $246.0661   $246.07   $246.05   $246.10  
  Purchase #6 $209.86   4.247%   $218.7728   $218.77   $218.75   $218.80  
  Purchase #7 $173.31   13.637%   $196.9443   $196.94   $196.95   $196.90  
  7 purchase totals = $1,201.34       $1,302.4148   $1,302.41   $1,302.35   $1,302.50