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	$247.49	10.309%	$273.0037	$273.00	$273.00	$273.00
Purchase #2	$78.81	4.512%	$82.3659	$82.37	$82.35	$82.40
Purchase #3	$92.38	13.821%	$105.1478	$105.15	$105.15	$105.10
Purchase #4	$19.89	7.671%	$21.4158	$21.42	$21.40	$21.40
Purchase #5	$38.38	12.517%	$43.184	$43.18	$43.20	$43.20
Purchase #6	$69.65	12.344%	$78.2476	$78.25	$78.25	$78.20
Purchase #7	$61.26	4.839%	$64.2244	$64.22	$64.20	$64.20
7 purchase totals =	$607.86		$667.5892	$667.59	$667.55	$667.50