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	$38.77	3.227%	$40.0211	$40.02	$40.00	$40.00
Purchase #2	$168.30	9.162%	$183.7196	$183.72	$183.70	$183.70
Purchase #3	$188.98	3.107%	$194.8516	$194.85	$194.85	$194.90
Purchase #4	$142.96	9.602%	$156.687	$156.69	$156.70	$156.70
Purchase #5	$229.66	6.213%	$243.9288	$243.93	$243.95	$243.90
Purchase #6	$205.56	13.388%	$233.0804	$233.08	$233.10	$233.10
Purchase #7	$137.55	6.713%	$146.7837	$146.78	$146.80	$146.80
7 purchase totals =	$1,111.78		$1,199.0722	$1,199.07	$1,199.10	$1,199.10