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 $187.65   11.376%   $208.9971   $209.00   $209.00   $209.00  
  Purchase #2 $60.97   5.382%   $64.2514   $64.25   $64.25   $64.30  
  Purchase #3 $169.49   9.172%   $185.0356   $185.04   $185.05   $185.00  
  Purchase #4 $178.33   10.386%   $196.8514   $196.85   $196.85   $196.90  
  Purchase #5 $125.45   5.712%   $132.6157   $132.62   $132.60   $132.60  
  Purchase #6 $87.79   8.681%   $95.411   $95.41   $95.40   $95.40  
  Purchase #7 $85.97   8.723%   $93.4692   $93.47   $93.45   $93.50  
  7 purchase totals = $895.65       $976.6314   $976.64   $976.60   $976.70