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 $181.88   12.869%   $205.2861   $205.29   $205.30   $205.30  
  Purchase #2 $223.76   4.329%   $233.4466   $233.45   $233.45   $233.40  
  Purchase #3 $21.26   4.558%   $22.229   $22.23   $22.25   $22.20  
  Purchase #4 $91.96   12.190%   $103.1699   $103.17   $103.15   $103.20  
  Purchase #5 $240.88   8.845%   $262.1858   $262.19   $262.20   $262.20  
  Purchase #6 $75.69   10.685%   $83.7775   $83.78   $83.80   $83.80  
  Purchase #7 $20.95   11.873%   $23.4374   $23.44   $23.45   $23.40  
  7 purchase totals = $856.38       $933.5323   $933.55   $933.60   $933.50