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 $187.77   8.206%   $203.1784   $203.18   $203.20   $203.20  
  Purchase #2 $153.57   11.313%   $170.9434   $170.94   $170.95   $170.90  
  Purchase #3 $76.41   12.646%   $86.0728   $86.07   $86.05   $86.10  
  Purchase #4 $210.89   13.420%   $239.1914   $239.19   $239.20   $239.20  
  Purchase #5 $207.32   6.600%   $221.0031   $221.00   $221.00   $221.00  
  Purchase #6 $126.28   9.205%   $137.9041   $137.90   $137.90   $137.90  
  Purchase #7 $101.83   13.541%   $115.6188   $115.62   $115.60   $115.60  
  7 purchase totals = $1,064.07       $1,173.9120   $1,173.90   $1,173.90   $1,173.90