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 $239.47   10.240%   $263.9917   $263.99   $264.00   $264.00  
  Purchase #2 $121.48   8.326%   $131.5944   $131.59   $131.60   $131.60  
  Purchase #3 $26.72   11.834%   $29.882   $29.88   $29.90   $29.90  
  Purchase #4 $156.45   11.139%   $173.877   $173.88   $173.90   $173.90  
  Purchase #5 $124.84   11.579%   $139.2952   $139.30   $139.30   $139.30  
  Purchase #6 $225.83   9.865%   $248.1081   $248.11   $248.10   $248.10  
  Purchase #7 $165.33   5.665%   $174.6959   $174.70   $174.70   $174.70  
  7 purchase totals = $1,060.12       $1,161.4443   $1,161.45   $1,161.50   $1,161.50