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	$232.39	13.713%	$264.2576	$264.26	$264.25	$264.30
Purchase #2	$73.53	11.732%	$82.1565	$82.16	$82.15	$82.20
Purchase #3	$71.31	7.307%	$76.5206	$76.52	$76.50	$76.50
Purchase #4	$88.79	11.180%	$98.7167	$98.72	$98.70	$98.70
Purchase #5	$223.32	9.250%	$243.9771	$243.98	$244.00	$244.00
Purchase #6	$51.31	6.456%	$54.6226	$54.62	$54.60	$54.60
Purchase #7	$56.55	4.854%	$59.2949	$59.29	$59.30	$59.30
7 purchase totals =	$797.20		$879.5460	$879.55	$879.50	$879.60