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 $61.30   12.116%   $68.7271   $68.73   $68.75   $68.70  
  Purchase #2 $54.29   12.103%   $60.8607   $60.86   $60.85   $60.90  
  Purchase #3 $61.34   11.662%   $68.4935   $68.49   $68.50   $68.50  
  Purchase #4 $181.93   8.786%   $197.9144   $197.91   $197.90   $197.90  
  Purchase #5 $218.53   3.382%   $225.9207   $225.92   $225.90   $225.90  
  Purchase #6 $102.31   5.436%   $107.8716   $107.87   $107.85   $107.90  
  Purchase #7 $244.62   8.492%   $265.3931   $265.39   $265.40   $265.40  
  7 purchase totals = $924.32       $995.1811   $995.17   $995.15   $995.20