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	$150.55	11.677%	$168.1297	$168.13	$168.15	$168.10
Purchase #2	$96.43	13.854%	$109.7894	$109.79	$109.80	$109.80
Purchase #3	$242.77	6.718%	$259.0793	$259.08	$259.10	$259.10
Purchase #4	$98.83	7.536%	$106.2778	$106.28	$106.30	$106.30
Purchase #5	$88.36	6.514%	$94.1158	$94.12	$94.10	$94.10
Purchase #6	$106.66	4.506%	$111.4661	$111.47	$111.45	$111.50
Purchase #7	$138.45	10.838%	$153.4552	$153.46	$153.45	$153.50
7 purchase totals =	$922.05		$1,002.3133	$1,002.33	$1,002.35	$1,002.40