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	$55.38	6.237%	$58.8341	$58.83	$58.85	$58.80
Purchase #2	$29.47	10.805%	$32.6542	$32.65	$32.65	$32.70
Purchase #3	$81.83	9.834%	$89.8772	$89.88	$89.90	$89.90
Purchase #4	$205.40	8.527%	$222.9145	$222.91	$222.90	$222.90
Purchase #5	$245.46	4.346%	$256.1277	$256.13	$256.15	$256.10
Purchase #6	$128.66	9.763%	$141.2211	$141.22	$141.20	$141.20
Purchase #7	$42.55	4.110%	$44.2988	$44.30	$44.30	$44.30
7 purchase totals =	$788.75		$845.9276	$845.92	$845.95	$845.90