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 $12.83   13.781%   $14.5981   $14.60   $14.60   $14.60  
  Purchase #2 $211.36   8.602%   $229.5412   $229.54   $229.55   $229.50  
  Purchase #3 $68.29   6.438%   $72.6865   $72.69   $72.70   $72.70  
  Purchase #4 $179.80   13.392%   $203.8788   $203.88   $203.90   $203.90  
  Purchase #5 $61.83   13.533%   $70.1975   $70.20   $70.20   $70.20  
  Purchase #6 $112.96   3.783%   $117.2333   $117.23   $117.25   $117.20  
  Purchase #7 $59.30   8.873%   $64.5617   $64.56   $64.55   $64.60  
  7 purchase totals = $706.37       $772.6971   $772.70   $772.75   $772.70