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 $67.97   8.396%   $73.6768   $73.68   $73.70   $73.70  
  Purchase #2 $230.83   7.809%   $248.8555   $248.86   $248.85   $248.90  
  Purchase #3 $152.39   6.354%   $162.0729   $162.07   $162.05   $162.10  
  Purchase #4 $74.85   12.179%   $83.966   $83.97   $83.95   $84.00  
  Purchase #5 $218.70   5.579%   $230.9013   $230.90   $230.90   $230.90  
  Purchase #6 $25.26   12.465%   $28.4087   $28.41   $28.40   $28.40  
  Purchase #7 $18.46   4.185%   $19.2326   $19.23   $19.25   $19.20  
  7 purchase totals = $788.46       $847.1138   $847.12   $847.10   $847.20