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	$229.98	11.630%	$256.7267	$256.73	$256.75	$256.70
Purchase #2	$24.65	11.130%	$27.3935	$27.39	$27.40	$27.40
Purchase #3	$216.41	12.583%	$243.6409	$243.64	$243.65	$243.60
Purchase #4	$32.30	4.698%	$33.8175	$33.82	$33.80	$33.80
Purchase #5	$6.88	8.216%	$7.4453	$7.45	$7.45	$7.40
Purchase #6	$111.65	10.299%	$123.1488	$123.15	$123.15	$123.10
Purchase #7	$114.84	13.442%	$130.2768	$130.28	$130.30	$130.30
7 purchase totals =	$736.71		$822.4495	$822.46	$822.50	$822.30