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	$129.98	6.744%	$138.7459	$138.75	$138.75	$138.70
Purchase #2	$89.97	10.364%	$99.2945	$99.29	$99.30	$99.30
Purchase #3	$56.82	10.296%	$62.6702	$62.67	$62.65	$62.70
Purchase #4	$144.41	6.243%	$153.4255	$153.43	$153.45	$153.40
Purchase #5	$218.46	11.473%	$243.5239	$243.52	$243.50	$243.50
Purchase #6	$139.66	4.609%	$146.0969	$146.10	$146.10	$146.10
Purchase #7	$145.40	9.516%	$159.2363	$159.24	$159.25	$159.20
7 purchase totals =	$924.70		$1,002.9932	$1,003.00	$1,003.00	$1,002.90