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 $86.61   10.658%   $95.8409   $95.84   $95.85   $95.80  
  Purchase #2 $5.72   13.813%   $6.5101   $6.51   $6.50   $6.50  
  Purchase #3 $186.95   7.322%   $200.6385   $200.64   $200.65   $200.60  
  Purchase #4 $245.66   4.179%   $255.9261   $255.93   $255.95   $255.90  
  Purchase #5 $210.95   10.271%   $232.6167   $232.62   $232.60   $232.60  
  Purchase #6 $195.81   5.154%   $205.902   $205.90   $205.90   $205.90  
  Purchase #7 $129.78   8.755%   $141.1422   $141.14   $141.15   $141.10  
  7 purchase totals = $1,061.48       $1,138.5765   $1,138.58   $1,138.60   $1,138.40