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 $87.70   8.127%   $94.8274   $94.83   $94.85   $94.80  
  Purchase #2 $142.86   4.205%   $148.8673   $148.87   $148.85   $148.90  
  Purchase #3 $39.37   13.714%   $44.7692   $44.77   $44.75   $44.80  
  Purchase #4 $22.66   7.760%   $24.4184   $24.42   $24.40   $24.40  
  Purchase #5 $192.25   7.709%   $207.0706   $207.07   $207.05   $207.10  
  Purchase #6 $198.75   5.225%   $209.1347   $209.13   $209.15   $209.10  
  Purchase #7 $30.43   13.619%   $34.5743   $34.57   $34.55   $34.60  
  7 purchase totals = $714.02       $763.6619   $763.66   $763.60   $763.70