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 $152.50   8.662%   $165.7096   $165.71   $165.70   $165.70  
  Purchase #2 $239.70   11.476%   $267.208   $267.21   $267.20   $267.20  
  Purchase #3 $24.76   11.849%   $27.6938   $27.69   $27.70   $27.70  
  Purchase #4 $60.80   6.771%   $64.9168   $64.92   $64.90   $64.90  
  Purchase #5 $224.88   11.567%   $250.8919   $250.89   $250.90   $250.90  
  Purchase #6 $87.82   8.228%   $95.0458   $95.05   $95.05   $95.00  
  Purchase #7 $206.83   3.834%   $214.7599   $214.76   $214.75   $214.80  
  7 purchase totals = $997.29       $1,086.2258   $1,086.23   $1,086.20   $1,086.20