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	$6.64	13.268%	$7.521	$7.52	$7.50	$7.50
Purchase #2	$226.90	11.570%	$253.1523	$253.15	$253.15	$253.20
Purchase #3	$74.99	11.298%	$83.4624	$83.46	$83.45	$83.50
Purchase #4	$21.26	4.292%	$22.1725	$22.17	$22.15	$22.20
Purchase #5	$200.38	7.599%	$215.6069	$215.61	$215.60	$215.60
Purchase #6	$225.52	6.182%	$239.4616	$239.46	$239.45	$239.50
Purchase #7	$189.79	3.210%	$195.8823	$195.88	$195.90	$195.90
7 purchase totals =	$945.48		$1,017.2590	$1,017.25	$1,017.20	$1,017.40