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	$83.73	10.812%	$92.7829	$92.78	$92.80	$92.80
Purchase #2	$123.26	13.501%	$139.9013	$139.90	$139.90	$139.90
Purchase #3	$139.94	13.520%	$158.8599	$158.86	$158.85	$158.90
Purchase #4	$185.86	13.108%	$210.2225	$210.22	$210.20	$210.20
Purchase #5	$209.78	11.316%	$233.5187	$233.52	$233.50	$233.50
Purchase #6	$250.96	3.830%	$260.5718	$260.57	$260.55	$260.60
Purchase #7	$241.99	12.525%	$272.2992	$272.30	$272.30	$272.30
7 purchase totals =	$1,235.52		$1,368.1563	$1,368.15	$1,368.10	$1,368.20