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	$58.37	10.754%	$64.6471	$64.65	$64.65	$64.60
Purchase #2	$241.72	4.674%	$253.018	$253.02	$253.00	$253.00
Purchase #3	$82.89	4.152%	$86.3316	$86.33	$86.35	$86.30
Purchase #4	$68.94	13.595%	$78.3124	$78.31	$78.30	$78.30
Purchase #5	$203.30	11.468%	$226.6144	$226.61	$226.60	$226.60
Purchase #6	$107.32	4.199%	$111.8264	$111.83	$111.85	$111.80
Purchase #7	$73.48	6.729%	$78.4245	$78.42	$78.40	$78.40
7 purchase totals =	$836.02		$899.1744	$899.17	$899.15	$899.00