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 $87.35   8.391%   $94.6795   $94.68   $94.70   $94.70  
  Purchase #2 $93.94   4.826%   $98.4735   $98.47   $98.45   $98.50  
  Purchase #3 $173.90   3.857%   $180.6073   $180.61   $180.60   $180.60  
  Purchase #4 $31.67   11.229%   $35.2262   $35.23   $35.25   $35.20  
  Purchase #5 $236.88   12.357%   $266.1513   $266.15   $266.15   $266.20  
  Purchase #6 $49.33   12.825%   $55.6566   $55.66   $55.65   $55.70  
  Purchase #7 $159.74   10.214%   $176.0558   $176.06   $176.05   $176.10  
  7 purchase totals = $832.81       $906.8502   $906.86   $906.85   $907.00