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 $88.92   3.617%   $92.1362   $92.14   $92.15   $92.10  
  Purchase #2 $84.35   12.615%   $94.9908   $94.99   $95.00   $95.00  
  Purchase #3 $195.34   11.806%   $218.4018   $218.40   $218.40   $218.40  
  Purchase #4 $137.43   11.733%   $153.5547   $153.55   $153.55   $153.60  
  Purchase #5 $50.61   9.443%   $55.3891   $55.39   $55.40   $55.40  
  Purchase #6 $193.50   4.854%   $202.8925   $202.89   $202.90   $202.90  
  Purchase #7 $247.64   4.135%   $257.8799   $257.88   $257.90   $257.90  
  7 purchase totals = $997.79       $1,075.2450   $1,075.24   $1,075.30   $1,075.30