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 $165.53   9.446%   $181.166   $181.17   $181.15   $181.20  
  Purchase #2 $95.60   3.136%   $98.598   $98.60   $98.60   $98.60  
  Purchase #3 $173.75   13.708%   $197.5677   $197.57   $197.55   $197.60  
  Purchase #4 $162.46   8.173%   $175.7379   $175.74   $175.75   $175.70  
  Purchase #5 $244.65   3.229%   $252.5497   $252.55   $252.55   $252.50  
  Purchase #6 $158.81   9.247%   $173.4952   $173.50   $173.50   $173.50  
  Purchase #7 $208.73   8.136%   $225.7123   $225.71   $225.70   $225.70  
  7 purchase totals = $1,209.53       $1,304.8268   $1,304.84   $1,304.80   $1,304.80