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 $228.86   10.108%   $251.9932   $251.99   $252.00   $252.00  
  Purchase #2 $236.99   9.442%   $259.3666   $259.37   $259.35   $259.40  
  Purchase #3 $108.94   6.599%   $116.129   $116.13   $116.15   $116.10  
  Purchase #4 $83.28   7.311%   $89.3686   $89.37   $89.35   $89.40  
  Purchase #5 $139.27   11.721%   $155.5938   $155.59   $155.60   $155.60  
  Purchase #6 $224.85   10.695%   $248.8977   $248.90   $248.90   $248.90  
  Purchase #7 $178.92   3.606%   $185.3719   $185.37   $185.35   $185.40  
  7 purchase totals = $1,201.11       $1,306.7208   $1,306.72   $1,306.70   $1,306.80