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 $161.92   7.249%   $173.6576   $173.66   $173.65   $173.70  
  Purchase #2 $176.86   8.760%   $192.3529   $192.35   $192.35   $192.40  
  Purchase #3 $228.90   7.774%   $246.6947   $246.69   $246.70   $246.70  
  Purchase #4 $53.46   5.828%   $56.5756   $56.58   $56.60   $56.60  
  Purchase #5 $234.77   6.433%   $249.8728   $249.87   $249.85   $249.90  
  Purchase #6 $202.91   8.849%   $220.8655   $220.87   $220.85   $220.90  
  Purchase #7 $95.73   9.722%   $105.0369   $105.04   $105.05   $105.00  
  7 purchase totals = $1,154.55       $1,245.0560   $1,245.06   $1,245.05   $1,245.20