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 $57.97   8.699%   $63.0128   $63.01   $63.00   $63.00  
  Purchase #2 $187.45   10.401%   $206.9467   $206.95   $206.95   $206.90  
  Purchase #3 $26.87   7.744%   $28.9508   $28.95   $28.95   $29.00  
  Purchase #4 $9.75   5.154%   $10.2525   $10.25   $10.25   $10.30  
  Purchase #5 $17.31   9.686%   $18.9866   $18.99   $19.00   $19.00  
  Purchase #6 $77.92   11.242%   $86.6798   $86.68   $86.70   $86.70  
  Purchase #7 $236.62   6.373%   $251.6998   $251.70   $251.70   $251.70  
  7 purchase totals = $613.89       $666.5290   $666.53   $666.55   $666.60