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 $31.35   13.477%   $35.575   $35.58   $35.60   $35.60  
  Purchase #2 $59.43   3.822%   $61.7014   $61.70   $61.70   $61.70  
  Purchase #3 $57.81   11.859%   $64.6657   $64.67   $64.65   $64.70  
  Purchase #4 $210.69   8.242%   $228.0551   $228.06   $228.05   $228.10  
  Purchase #5 $140.91   7.138%   $150.9682   $150.97   $150.95   $151.00  
  Purchase #6 $77.62   8.497%   $84.2154   $84.22   $84.20   $84.20  
  Purchase #7 $97.49   5.662%   $103.0099   $103.01   $103.00   $103.00  
  7 purchase totals = $675.30       $728.1907   $728.21   $728.15   $728.30