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 $116.38   8.297%   $126.036   $126.04   $126.05   $126.00  
  Purchase #2 $108.49   4.145%   $112.9869   $112.99   $113.00   $113.00  
  Purchase #3 $83.98   11.163%   $93.3547   $93.35   $93.35   $93.40  
  Purchase #4 $165.34   8.862%   $179.9924   $179.99   $180.00   $180.00  
  Purchase #5 $222.25   10.376%   $245.3107   $245.31   $245.30   $245.30  
  Purchase #6 $126.95   9.671%   $139.2273   $139.23   $139.25   $139.20  
  Purchase #7 $69.69   3.690%   $72.2616   $72.26   $72.25   $72.30  
  7 purchase totals = $893.08       $969.1696   $969.17   $969.20   $969.20