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 $247.71   10.635%   $274.054   $274.05   $274.05   $274.10  
  Purchase #2 $104.45   8.855%   $113.699   $113.70   $113.70   $113.70  
  Purchase #3 $172.99   3.401%   $178.8734   $178.87   $178.85   $178.90  
  Purchase #4 $238.27   6.845%   $254.5796   $254.58   $254.60   $254.60  
  Purchase #5 $147.37   13.774%   $167.6687   $167.67   $167.65   $167.70  
  Purchase #6 $166.49   4.858%   $174.5781   $174.58   $174.60   $174.60  
  Purchase #7 $182.53   9.312%   $199.5272   $199.53   $199.55   $199.50  
  7 purchase totals = $1,259.81       $1,362.9800   $1,362.98   $1,363.00   $1,363.10