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 $248.64   7.507%   $267.3054   $267.31   $267.30   $267.30  
  Purchase #2 $86.93   12.539%   $97.8302   $97.83   $97.85   $97.80  
  Purchase #3 $180.53   12.229%   $202.607   $202.61   $202.60   $202.60  
  Purchase #4 $112.31   12.598%   $126.4588   $126.46   $126.45   $126.50  
  Purchase #5 $182.76   4.189%   $190.4158   $190.42   $190.40   $190.40  
  Purchase #6 $248.45   7.489%   $267.0564   $267.06   $267.05   $267.10  
  Purchase #7 $184.85   5.657%   $195.307   $195.31   $195.30   $195.30  
  7 purchase totals = $1,244.47       $1,346.9806   $1,347.00   $1,346.95   $1,347.00