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 $119.25   3.376%   $123.2759   $123.28   $123.30   $123.30  
  Purchase #2 $21.88   9.114%   $23.8741   $23.87   $23.85   $23.90  
  Purchase #3 $241.63   13.495%   $274.238   $274.24   $274.25   $274.20  
  Purchase #4 $18.39   4.214%   $19.165   $19.17   $19.15   $19.20  
  Purchase #5 $52.68   11.214%   $58.5875   $58.59   $58.60   $58.60  
  Purchase #6 $216.61   4.343%   $226.0174   $226.02   $226.00   $226.00  
  Purchase #7 $241.91   11.536%   $269.8167   $269.82   $269.80   $269.80  
  7 purchase totals = $912.35       $994.9746   $994.99   $994.95   $995.00