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 $61.70   12.227%   $69.2441   $69.24   $69.25   $69.20  
  Purchase #2 $196.31   10.621%   $217.1601   $217.16   $217.15   $217.20  
  Purchase #3 $21.45   11.492%   $23.915   $23.92   $23.90   $23.90  
  Purchase #4 $181.85   4.275%   $189.6241   $189.62   $189.60   $189.60  
  Purchase #5 $162.46   3.844%   $168.705   $168.71   $168.70   $168.70  
  Purchase #6 $98.35   6.212%   $104.4595   $104.46   $104.45   $104.50  
  Purchase #7 $216.31   4.753%   $226.5912   $226.59   $226.60   $226.60  
  7 purchase totals = $938.43       $999.6990   $999.70   $999.65   $999.70