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 $239.87   10.273%   $264.5118   $264.51   $264.50   $264.50  
  Purchase #2 $76.53   9.461%   $83.7705   $83.77   $83.75   $83.80  
  Purchase #3 $128.65   6.379%   $136.8566   $136.86   $136.85   $136.90  
  Purchase #4 $204.98   6.244%   $217.779   $217.78   $217.80   $217.80  
  Purchase #5 $161.60   11.786%   $180.6462   $180.65   $180.65   $180.60  
  Purchase #6 $102.73   11.641%   $114.6888   $114.69   $114.70   $114.70  
  Purchase #7 $157.28   13.587%   $178.6496   $178.65   $178.65   $178.60  
  7 purchase totals = $1,071.64       $1,176.9025   $1,176.91   $1,176.90   $1,176.90