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 $205.75   6.513%   $219.1505   $219.15   $219.15   $219.20  
  Purchase #2 $208.95   8.130%   $225.9376   $225.94   $225.95   $225.90  
  Purchase #3 $222.91   11.168%   $247.8046   $247.80   $247.80   $247.80  
  Purchase #4 $14.99   12.494%   $16.8629   $16.86   $16.85   $16.90  
  Purchase #5 $59.27   10.696%   $65.6095   $65.61   $65.60   $65.60  
  Purchase #6 $9.29   9.284%   $10.1525   $10.15   $10.15   $10.20  
  Purchase #7 $214.77   12.345%   $241.2834   $241.28   $241.30   $241.30  
  7 purchase totals = $935.93       $1,026.8010   $1,026.79   $1,026.80   $1,026.90