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 $81.59   13.537%   $92.6348   $92.63   $92.65   $92.60  
  Purchase #2 $132.84   7.382%   $142.6462   $142.65   $142.65   $142.60  
  Purchase #3 $184.98   7.867%   $199.5324   $199.53   $199.55   $199.50  
  Purchase #4 $77.58   12.331%   $87.1464   $87.15   $87.15   $87.10  
  Purchase #5 $164.35   4.524%   $171.7852   $171.79   $171.80   $171.80  
  Purchase #6 $115.69   13.247%   $131.0155   $131.02   $131.00   $131.00  
  Purchase #7 $200.99   8.827%   $218.7314   $218.73   $218.75   $218.70  
  7 purchase totals = $958.02       $1,043.4919   $1,043.50   $1,043.55   $1,043.30