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	$202.92	13.254%	$229.815	$229.82	$229.80	$229.80
Purchase #2	$51.60	3.518%	$53.4153	$53.42	$53.40	$53.40
Purchase #3	$75.30	4.797%	$78.9121	$78.91	$78.90	$78.90
Purchase #4	$133.36	9.718%	$146.3199	$146.32	$146.30	$146.30
Purchase #5	$69.54	9.681%	$76.2722	$76.27	$76.25	$76.30
Purchase #6	$92.25	12.562%	$103.8384	$103.84	$103.85	$103.80
Purchase #7	$120.73	10.595%	$133.5213	$133.52	$133.50	$133.50
7 purchase totals =	$745.70		$822.0942	$822.10	$822.00	$822.00