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 $215.99   10.513%   $238.697   $238.70   $238.70   $238.70  
  Purchase #2 $69.86   10.322%   $77.0709   $77.07   $77.05   $77.10  
  Purchase #3 $243.89   5.658%   $257.6893   $257.69   $257.70   $257.70  
  Purchase #4 $178.29   8.809%   $193.9956   $194.00   $194.00   $194.00  
  Purchase #5 $131.48   11.706%   $146.871   $146.87   $146.85   $146.90  
  Purchase #6 $238.49   4.131%   $248.342   $248.34   $248.35   $248.30  
  Purchase #7 $194.81   13.840%   $221.7717   $221.77   $221.75   $221.80  
  7 purchase totals = $1,272.81       $1,384.4375   $1,384.44   $1,384.40   $1,384.50