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 $126.91   13.326%   $143.822   $143.82   $143.80   $143.80  
  Purchase #2 $65.95   6.632%   $70.3238   $70.32   $70.30   $70.30  
  Purchase #3 $153.74   13.117%   $173.9061   $173.91   $173.90   $173.90  
  Purchase #4 $36.69   7.791%   $39.5485   $39.55   $39.55   $39.50  
  Purchase #5 $14.70   6.391%   $15.6395   $15.64   $15.65   $15.60  
  Purchase #6 $72.27   7.706%   $77.8391   $77.84   $77.85   $77.80  
  Purchase #7 $208.49   12.496%   $234.5429   $234.54   $234.55   $234.50  
  7 purchase totals = $678.75       $755.6219   $755.62   $755.60   $755.40