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 $92.52   11.597%   $103.2495   $103.25   $103.25   $103.20  
  Purchase #2 $142.41   11.541%   $158.8455   $158.85   $158.85   $158.80  
  Purchase #3 $34.25   7.556%   $36.8379   $36.84   $36.85   $36.80  
  Purchase #4 $243.44   4.408%   $254.1708   $254.17   $254.15   $254.20  
  Purchase #5 $118.81   6.129%   $126.0919   $126.09   $126.10   $126.10  
  Purchase #6 $79.69   7.831%   $85.9305   $85.93   $85.95   $85.90  
  Purchase #7 $55.71   10.706%   $61.6743   $61.67   $61.65   $61.70  
  7 purchase totals = $766.83       $826.8004   $826.80   $826.80   $826.70