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	$170.94	7.772%	$184.2255	$184.23	$184.25	$184.20
Purchase #2	$127.38	12.756%	$143.6286	$143.63	$143.65	$143.60
Purchase #3	$15.41	4.302%	$16.0729	$16.07	$16.05	$16.10
Purchase #4	$139.69	4.203%	$145.5612	$145.56	$145.55	$145.60
Purchase #5	$79.43	12.696%	$89.5144	$89.51	$89.50	$89.50
Purchase #6	$91.44	5.520%	$96.4875	$96.49	$96.50	$96.50
Purchase #7	$53.82	3.774%	$55.8512	$55.85	$55.85	$55.90
7 purchase totals =	$678.11		$731.3413	$731.34	$731.35	$731.40