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 $150.54   7.128%   $161.2705   $161.27   $161.25   $161.30  
  Purchase #2 $69.87   8.500%   $75.809   $75.81   $75.80   $75.80  
  Purchase #3 $164.84   12.800%   $185.9395   $185.94   $185.95   $185.90  
  Purchase #4 $28.51   10.471%   $31.4953   $31.50   $31.50   $31.50  
  Purchase #5 $10.58   3.644%   $10.9655   $10.97   $10.95   $11.00  
  Purchase #6 $53.47   8.716%   $58.1304   $58.13   $58.15   $58.10  
  Purchase #7 $121.74   4.737%   $127.5068   $127.51   $127.50   $127.50  
  7 purchase totals = $599.55       $651.1170   $651.13   $651.10   $651.10