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 $207.29   13.480%   $235.2327   $235.23   $235.25   $235.20  
  Purchase #2 $196.43   7.784%   $211.7201   $211.72   $211.70   $211.70  
  Purchase #3 $59.60   12.308%   $66.9356   $66.94   $66.95   $66.90  
  Purchase #4 $15.81   5.269%   $16.643   $16.64   $16.65   $16.60  
  Purchase #5 $72.60   6.454%   $77.2856   $77.29   $77.30   $77.30  
  Purchase #6 $237.66   10.743%   $263.1918   $263.19   $263.20   $263.20  
  Purchase #7 $191.77   11.675%   $214.1591   $214.16   $214.15   $214.20  
  7 purchase totals = $981.16       $1,085.1679   $1,085.17   $1,085.20   $1,085.10