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	$54.55	8.599%	$59.2408	$59.24	$59.25	$59.20
Purchase #2	$125.25	3.700%	$129.8843	$129.88	$129.90	$129.90
Purchase #3	$75.84	3.747%	$78.6817	$78.68	$78.70	$78.70
Purchase #4	$80.42	10.595%	$88.9405	$88.94	$88.95	$88.90
Purchase #5	$227.65	6.375%	$242.1627	$242.16	$242.15	$242.20
Purchase #6	$171.91	13.281%	$194.7414	$194.74	$194.75	$194.70
Purchase #7	$67.47	7.171%	$72.3083	$72.31	$72.30	$72.30
7 purchase totals =	$803.09		$865.9597	$865.95	$866.00	$865.90