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	$61.94	13.278%	$70.1644	$70.16	$70.15	$70.20
Purchase #2	$245.38	10.643%	$271.4958	$271.50	$271.50	$271.50
Purchase #3	$91.31	9.528%	$100.01	$100.01	$100.00	$100.00
Purchase #4	$162.56	9.842%	$178.5592	$178.56	$178.55	$178.60
Purchase #5	$191.43	6.398%	$203.6777	$203.68	$203.70	$203.70
Purchase #6	$79.92	12.570%	$89.9659	$89.97	$89.95	$90.00
Purchase #7	$100.46	7.444%	$107.9382	$107.94	$107.95	$107.90
7 purchase totals =	$933.00		$1,021.8112	$1,021.82	$1,021.80	$1,021.90