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	$128.40	6.858%	$137.2057	$137.21	$137.20	$137.20
Purchase #2	$107.47	3.458%	$111.1863	$111.19	$111.20	$111.20
Purchase #3	$137.83	6.700%	$147.0646	$147.06	$147.05	$147.10
Purchase #4	$99.97	9.217%	$109.1842	$109.18	$109.20	$109.20
Purchase #5	$17.66	9.111%	$19.269	$19.27	$19.25	$19.30
Purchase #6	$33.65	10.345%	$37.1311	$37.13	$37.15	$37.10
Purchase #7	$220.53	4.416%	$230.2686	$230.27	$230.25	$230.30
7 purchase totals =	$745.51		$791.3095	$791.31	$791.30	$791.40