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	$159.78	13.279%	$180.9972	$181.00	$181.00	$181.00
Purchase #2	$142.56	7.838%	$153.7339	$153.73	$153.75	$153.70
Purchase #3	$103.91	10.654%	$114.9806	$114.98	$115.00	$115.00
Purchase #4	$246.83	6.498%	$262.869	$262.87	$262.85	$262.90
Purchase #5	$86.45	5.814%	$91.4762	$91.48	$91.50	$91.50
Purchase #6	$220.84	6.105%	$234.3223	$234.32	$234.30	$234.30
Purchase #7	$99.87	11.594%	$111.4489	$111.45	$111.45	$111.40
7 purchase totals =	$1,060.24		$1,149.8281	$1,149.83	$1,149.85	$1,149.80