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 $247.54   7.561%   $266.2565   $266.26   $266.25   $266.30  
  Purchase #2 $165.63   7.156%   $177.4825   $177.48   $177.50   $177.50  
  Purchase #3 $56.54   7.323%   $60.6804   $60.68   $60.70   $60.70  
  Purchase #4 $217.48   4.651%   $227.595   $227.60   $227.60   $227.60  
  Purchase #5 $237.47   12.347%   $266.7904   $266.79   $266.80   $266.80  
  Purchase #6 $62.47   6.686%   $66.6467   $66.65   $66.65   $66.60  
  Purchase #7 $227.97   9.387%   $249.3695   $249.37   $249.35   $249.40  
  7 purchase totals = $1,215.10       $1,314.8210   $1,314.83   $1,314.85   $1,314.90