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 $73.67   4.290%   $76.8304   $76.83   $76.85   $76.80  
  Purchase #2 $145.83   10.572%   $161.2471   $161.25   $161.25   $161.20  
  Purchase #3 $48.31   11.281%   $53.7599   $53.76   $53.75   $53.80  
  Purchase #4 $88.56   7.735%   $95.4101   $95.41   $95.40   $95.40  
  Purchase #5 $199.65   7.203%   $214.0308   $214.03   $214.05   $214.00  
  Purchase #6 $199.73   4.109%   $207.9369   $207.94   $207.95   $207.90  
  Purchase #7 $163.81   12.371%   $184.0749   $184.07   $184.05   $184.10  
  7 purchase totals = $919.56       $993.2901   $993.29   $993.30   $993.20