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 $49.35   11.828%   $55.1871   $55.19   $55.20   $55.20  
  Purchase #2 $218.68   10.370%   $241.3571   $241.36   $241.35   $241.40  
  Purchase #3 $175.99   7.209%   $188.6771   $188.68   $188.70   $188.70  
  Purchase #4 $218.86   7.278%   $234.7886   $234.79   $234.80   $234.80  
  Purchase #5 $173.32   10.455%   $191.4406   $191.44   $191.45   $191.40  
  Purchase #6 $91.58   8.764%   $99.6061   $99.61   $99.60   $99.60  
  Purchase #7 $175.86   12.822%   $198.4088   $198.41   $198.40   $198.40  
  7 purchase totals = $1,103.64       $1,209.4654   $1,209.48   $1,209.50   $1,209.50