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 $89.69   4.341%   $93.5834   $93.58   $93.60   $93.60  
  Purchase #2 $200.34   8.166%   $216.6998   $216.70   $216.70   $216.70  
  Purchase #3 $138.87   11.350%   $154.6317   $154.63   $154.65   $154.60  
  Purchase #4 $115.75   12.278%   $129.9618   $129.96   $129.95   $130.00  
  Purchase #5 $83.54   5.387%   $88.0403   $88.04   $88.05   $88.00  
  Purchase #6 $135.86   13.387%   $154.0476   $154.05   $154.05   $154.00  
  Purchase #7 $230.71   13.663%   $262.2319   $262.23   $262.25   $262.20  
  7 purchase totals = $994.76       $1,099.1965   $1,099.19   $1,099.25   $1,099.10