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	$199.31	10.744%	$220.7239	$220.72	$220.70	$220.70
Purchase #2	$86.47	5.351%	$91.097	$91.10	$91.10	$91.10
Purchase #3	$108.77	11.104%	$120.8478	$120.85	$120.85	$120.80
Purchase #4	$235.66	8.808%	$256.4169	$256.42	$256.40	$256.40
Purchase #5	$95.73	3.582%	$99.159	$99.16	$99.15	$99.20
Purchase #6	$181.86	6.823%	$194.2683	$194.27	$194.25	$194.30
Purchase #7	$88.65	12.192%	$99.4582	$99.46	$99.45	$99.50
7 purchase totals =	$996.45		$1,081.9711	$1,081.98	$1,081.90	$1,082.00