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 $42.99   4.807%   $45.0565   $45.06   $45.05   $45.10  
  Purchase #2 $74.67   10.150%   $82.249   $82.25   $82.25   $82.20  
  Purchase #3 $85.33   8.247%   $92.3672   $92.37   $92.35   $92.40  
  Purchase #4 $34.85   9.302%   $38.0917   $38.09   $38.10   $38.10  
  Purchase #5 $245.73   3.852%   $255.1955   $255.20   $255.20   $255.20  
  Purchase #6 $9.58   8.548%   $10.3989   $10.40   $10.40   $10.40  
  Purchase #7 $32.36   7.490%   $34.7838   $34.78   $34.80   $34.80  
  7 purchase totals = $525.51       $558.1426   $558.15   $558.15   $558.20