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 $164.26   12.816%   $185.3116   $185.31   $185.30   $185.30  
  Purchase #2 $119.36   12.544%   $134.3325   $134.33   $134.35   $134.30  
  Purchase #3 $232.68   11.459%   $259.3428   $259.34   $259.35   $259.30  
  Purchase #4 $206.99   4.473%   $216.2487   $216.25   $216.25   $216.20  
  Purchase #5 $14.93   8.510%   $16.2005   $16.20   $16.20   $16.20  
  Purchase #6 $95.63   13.774%   $108.8021   $108.80   $108.80   $108.80  
  Purchase #7 $18.59   13.225%   $21.0485   $21.05   $21.05   $21.00  
  7 purchase totals = $852.44       $941.2867   $941.28   $941.30   $941.10