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 $94.83   11.854%   $106.0711   $106.07   $106.05   $106.10  
  Purchase #2 $15.53   5.855%   $16.4393   $16.44   $16.45   $16.40  
  Purchase #3 $250.59   13.634%   $284.7554   $284.76   $284.75   $284.80  
  Purchase #4 $27.95   8.561%   $30.3428   $30.34   $30.35   $30.30  
  Purchase #5 $128.96   8.456%   $139.8649   $139.86   $139.85   $139.90  
  Purchase #6 $193.76   13.525%   $219.966   $219.97   $219.95   $220.00  
  Purchase #7 $222.80   8.393%   $241.4996   $241.50   $241.50   $241.50  
  7 purchase totals = $934.42       $1,038.9391   $1,038.94   $1,038.90   $1,039.00