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 $17.48   7.835%   $18.8496   $18.85   $18.85   $18.80  
  Purchase #2 $196.44   9.597%   $215.2923   $215.29   $215.30   $215.30  
  Purchase #3 $9.47   12.640%   $10.667   $10.67   $10.65   $10.70  
  Purchase #4 $195.29   12.414%   $219.5333   $219.53   $219.55   $219.50  
  Purchase #5 $12.59   6.728%   $13.4371   $13.44   $13.45   $13.40  
  Purchase #6 $8.56   3.153%   $8.8299   $8.83   $8.85   $8.80  
  Purchase #7 $148.86   10.731%   $164.8342   $164.83   $164.85   $164.80  
  7 purchase totals = $588.69       $651.4434   $651.44   $651.50   $651.30