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	$56.29	5.304%	$59.2756	$59.28	$59.30	$59.30
Purchase #2	$58.76	11.606%	$65.5797	$65.58	$65.60	$65.60
Purchase #3	$115.68	13.171%	$130.9162	$130.92	$130.90	$130.90
Purchase #4	$178.73	9.687%	$196.0436	$196.04	$196.05	$196.00
Purchase #5	$229.59	11.834%	$256.7597	$256.76	$256.75	$256.80
Purchase #6	$132.25	9.316%	$144.5704	$144.57	$144.55	$144.60
Purchase #7	$36.69	9.684%	$40.2431	$40.24	$40.25	$40.20
7 purchase totals =	$807.99		$893.3883	$893.39	$893.40	$893.40