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	$98.82	10.413%	$109.1101	$109.11	$109.10	$109.10
Purchase #2	$189.92	8.286%	$205.6568	$205.66	$205.65	$205.70
Purchase #3	$37.52	10.368%	$41.4101	$41.41	$41.40	$41.40
Purchase #4	$210.36	3.723%	$218.1917	$218.19	$218.20	$218.20
Purchase #5	$38.51	10.725%	$42.6402	$42.64	$42.65	$42.60
Purchase #6	$46.47	11.753%	$51.9316	$51.93	$51.95	$51.90
Purchase #7	$51.91	6.575%	$55.3231	$55.32	$55.30	$55.30
7 purchase totals =	$673.51		$724.2636	$724.26	$724.25	$724.20