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	$36.29	6.666%	$38.7091	$38.71	$38.70	$38.70
Purchase #2	$86.75	6.163%	$92.0964	$92.10	$92.10	$92.10
Purchase #3	$145.92	13.506%	$165.628	$165.63	$165.65	$165.60
Purchase #4	$29.83	8.594%	$32.3936	$32.39	$32.40	$32.40
Purchase #5	$200.58	10.811%	$222.2647	$222.26	$222.25	$222.30
Purchase #6	$96.40	13.216%	$109.1402	$109.14	$109.15	$109.10
Purchase #7	$222.60	11.363%	$247.894	$247.89	$247.90	$247.90
7 purchase totals =	$818.37		$908.1260	$908.12	$908.15	$908.10