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 $37.33   12.277%   $41.913   $41.91   $41.90   $41.90  
  Purchase #2 $131.28   12.163%   $147.2476   $147.25   $147.25   $147.20  
  Purchase #3 $25.60   8.197%   $27.6984   $27.70   $27.70   $27.70  
  Purchase #4 $245.28   3.191%   $253.1069   $253.11   $253.10   $253.10  
  Purchase #5 $237.73   9.161%   $259.5084   $259.51   $259.50   $259.50  
  Purchase #6 $93.49   7.366%   $100.3765   $100.38   $100.40   $100.40  
  Purchase #7 $213.56   12.421%   $240.0863   $240.09   $240.10   $240.10  
  7 purchase totals = $984.27       $1,069.9371   $1,069.95   $1,069.95   $1,069.90