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 $61.96   4.226%   $64.5784   $64.58   $64.60   $64.60  
  Purchase #2 $173.69   6.627%   $185.2004   $185.20   $185.20   $185.20  
  Purchase #3 $83.27   4.518%   $87.0321   $87.03   $87.05   $87.00  
  Purchase #4 $29.86   8.312%   $32.342   $32.34   $32.35   $32.30  
  Purchase #5 $225.37   8.205%   $243.8616   $243.86   $243.85   $243.90  
  Purchase #6 $115.88   13.378%   $131.3824   $131.38   $131.40   $131.40  
  Purchase #7 $82.58   6.102%   $87.619   $87.62   $87.60   $87.60  
  7 purchase totals = $772.61       $832.0159   $832.01   $832.05   $832.00