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	$97.79	3.634%	$101.3437	$101.34	$101.35	$101.30
Purchase #2	$97.31	6.647%	$103.7782	$103.78	$103.80	$103.80
Purchase #3	$241.54	8.538%	$262.1627	$262.16	$262.15	$262.20
Purchase #4	$225.88	12.241%	$253.53	$253.53	$253.55	$253.50
Purchase #5	$145.63	6.607%	$155.2518	$155.25	$155.25	$155.30
Purchase #6	$80.88	5.560%	$85.3769	$85.38	$85.40	$85.40
Purchase #7	$240.51	11.625%	$268.4693	$268.47	$268.45	$268.50
7 purchase totals =	$1,129.54		$1,229.9126	$1,229.91	$1,229.95	$1,230.00