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	$30.64	3.441%	$31.6943	$31.69	$31.70	$31.70
Purchase #2	$192.48	13.680%	$218.8113	$218.81	$218.80	$218.80
Purchase #3	$242.96	11.287%	$270.3829	$270.38	$270.40	$270.40
Purchase #4	$52.48	12.429%	$59.0027	$59.00	$59.00	$59.00
Purchase #5	$117.63	5.390%	$123.9703	$123.97	$123.95	$124.00
Purchase #6	$175.26	5.681%	$185.2165	$185.22	$185.20	$185.20
Purchase #7	$50.26	7.159%	$53.8581	$53.86	$53.85	$53.90
7 purchase totals =	$861.71		$942.9361	$942.93	$942.90	$943.00