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	$174.96	5.156%	$183.9809	$183.98	$184.00	$184.00
Purchase #2	$33.57	13.860%	$38.2228	$38.22	$38.20	$38.20
Purchase #3	$78.93	8.637%	$85.7472	$85.75	$85.75	$85.70
Purchase #4	$103.95	7.191%	$111.425	$111.43	$111.45	$111.40
Purchase #5	$33.69	10.344%	$37.1749	$37.17	$37.15	$37.20
Purchase #6	$135.30	13.282%	$153.2705	$153.27	$153.25	$153.30
Purchase #7	$43.72	7.133%	$46.8385	$46.84	$46.85	$46.80
7 purchase totals =	$604.12		$656.6598	$656.66	$656.65	$656.60