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 $18.63   7.722%   $20.0686   $20.07   $20.05   $20.10  
  Purchase #2 $171.29   4.226%   $178.5287   $178.53   $178.55   $178.50  
  Purchase #3 $49.92   12.305%   $56.0627   $56.06   $56.05   $56.10  
  Purchase #4 $235.53   11.769%   $263.2495   $263.25   $263.25   $263.20  
  Purchase #5 $153.93   8.157%   $166.4861   $166.49   $166.50   $166.50  
  Purchase #6 $192.53   5.569%   $203.252   $203.25   $203.25   $203.30  
  Purchase #7 $209.25   7.339%   $224.6069   $224.61   $224.60   $224.60  
  7 purchase totals = $1,031.08       $1,112.2545   $1,112.26   $1,112.25   $1,112.30