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 $164.55   10.706%   $182.1667   $182.17   $182.15   $182.20  
  Purchase #2 $5.88   6.808%   $6.2803   $6.28   $6.30   $6.30  
  Purchase #3 $154.29   11.404%   $171.8852   $171.89   $171.90   $171.90  
  Purchase #4 $18.88   7.364%   $20.2703   $20.27   $20.25   $20.30  
  Purchase #5 $84.80   12.615%   $95.4975   $95.50   $95.50   $95.50  
  Purchase #6 $227.88   10.796%   $252.4819   $252.48   $252.50   $252.50  
  Purchase #7 $182.75   12.533%   $205.6541   $205.65   $205.65   $205.70  
  7 purchase totals = $839.03       $934.2360   $934.24   $934.25   $934.40