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 $65.49   7.697%   $70.5308   $70.53   $70.55   $70.50  
  Purchase #2 $180.86   8.524%   $196.2765   $196.28   $196.30   $196.30  
  Purchase #3 $41.43   6.298%   $44.0393   $44.04   $44.05   $44.00  
  Purchase #4 $98.65   6.175%   $104.7416   $104.74   $104.75   $104.70  
  Purchase #5 $238.47   4.247%   $248.5978   $248.60   $248.60   $248.60  
  Purchase #6 $8.68   11.224%   $9.6542   $9.65   $9.65   $9.70  
  Purchase #7 $173.48   11.103%   $192.7415   $192.74   $192.75   $192.70  
  7 purchase totals = $807.06       $866.5817   $866.58   $866.65   $866.50