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	$228.32	8.671%	$248.1176	$248.12	$248.10	$248.10
Purchase #2	$91.52	10.158%	$100.8166	$100.82	$100.80	$100.80
Purchase #3	$247.51	7.216%	$265.3703	$265.37	$265.35	$265.40
Purchase #4	$140.61	8.323%	$152.313	$152.31	$152.30	$152.30
Purchase #5	$102.66	13.869%	$116.8979	$116.90	$116.90	$116.90
Purchase #6	$149.30	4.813%	$156.4858	$156.49	$156.50	$156.50
Purchase #7	$250.82	3.780%	$260.301	$260.30	$260.30	$260.30
7 purchase totals =	$1,210.74		$1,300.3022	$1,300.31	$1,300.25	$1,300.30