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 $208.86   8.691%   $227.012   $227.01   $227.00   $227.00  
  Purchase #2 $166.80   6.439%   $177.5403   $177.54   $177.55   $177.50  
  Purchase #3 $125.73   3.277%   $129.8502   $129.85   $129.85   $129.90  
  Purchase #4 $197.63   9.524%   $216.4523   $216.45   $216.45   $216.50  
  Purchase #5 $198.27   9.146%   $216.4038   $216.40   $216.40   $216.40  
  Purchase #6 $178.30   10.440%   $196.9145   $196.91   $196.90   $196.90  
  Purchase #7 $38.28   11.609%   $42.7239   $42.72   $42.70   $42.70  
  7 purchase totals = $1,113.87       $1,206.8970   $1,206.88   $1,206.85   $1,206.90