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 $181.51   13.407%   $205.845   $205.85   $205.85   $205.80  
  Purchase #2 $69.88   9.269%   $76.3572   $76.36   $76.35   $76.40  
  Purchase #3 $162.40   12.477%   $182.6626   $182.66   $182.65   $182.70  
  Purchase #4 $189.68   12.317%   $213.0429   $213.04   $213.05   $213.00  
  Purchase #5 $205.63   12.145%   $230.6038   $230.60   $230.60   $230.60  
  Purchase #6 $34.93   12.195%   $39.1897   $39.19   $39.20   $39.20  
  Purchase #7 $171.54   7.420%   $184.2683   $184.27   $184.25   $184.30  
  7 purchase totals = $1,015.57       $1,131.9695   $1,131.97   $1,131.95   $1,132.00