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	$240.62	4.326%	$251.0292	$251.03	$251.05	$251.00
Purchase #2	$83.37	7.817%	$89.887	$89.89	$89.90	$89.90
Purchase #3	$47.39	13.187%	$53.6393	$53.64	$53.65	$53.60
Purchase #4	$19.90	6.308%	$21.1553	$21.16	$21.15	$21.20
Purchase #5	$136.51	13.244%	$154.5894	$154.59	$154.60	$154.60
Purchase #6	$220.26	10.269%	$242.8785	$242.88	$242.90	$242.90
Purchase #7	$67.31	9.238%	$73.5281	$73.53	$73.55	$73.50
7 purchase totals =	$815.36		$886.7068	$886.72	$886.80	$886.70