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 $204.97   7.376%   $220.0886   $220.09   $220.10   $220.10  
  Purchase #2 $205.71   5.455%   $216.9315   $216.93   $216.95   $216.90  
  Purchase #3 $73.44   9.381%   $80.3294   $80.33   $80.35   $80.30  
  Purchase #4 $71.57   11.400%   $79.729   $79.73   $79.75   $79.70  
  Purchase #5 $185.77   11.248%   $206.6654   $206.67   $206.65   $206.70  
  Purchase #6 $214.94   4.450%   $224.5048   $224.50   $224.50   $224.50  
  Purchase #7 $79.26   8.589%   $86.0676   $86.07   $86.05   $86.10  
  7 purchase totals = $1,035.66       $1,114.3163   $1,114.32   $1,114.35   $1,114.30