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	$53.71	8.523%	$58.2877	$58.29	$58.30	$58.30
Purchase #2	$44.73	12.849%	$50.4774	$50.48	$50.50	$50.50
Purchase #3	$230.63	6.190%	$244.906	$244.91	$244.90	$244.90
Purchase #4	$45.94	11.532%	$51.2378	$51.24	$51.25	$51.20
Purchase #5	$55.89	7.206%	$59.9174	$59.92	$59.90	$59.90
Purchase #6	$7.63	13.793%	$8.6824	$8.68	$8.70	$8.70
Purchase #7	$78.94	12.630%	$88.9101	$88.91	$88.90	$88.90
7 purchase totals =	$517.47		$562.4188	$562.43	$562.45	$562.40