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	$54.37	8.596%	$59.0436	$59.04	$59.05	$59.00
Purchase #2	$234.84	12.743%	$264.7657	$264.77	$264.75	$264.80
Purchase #3	$219.44	8.445%	$237.9717	$237.97	$237.95	$238.00
Purchase #4	$99.27	12.262%	$111.4425	$111.44	$111.45	$111.40
Purchase #5	$53.38	6.302%	$56.744	$56.74	$56.75	$56.70
Purchase #6	$6.57	11.361%	$7.3164	$7.32	$7.30	$7.30
Purchase #7	$57.95	10.649%	$64.1211	$64.12	$64.10	$64.10
7 purchase totals =	$725.82		$801.4050	$801.40	$801.35	$801.30