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	$204.36	12.705%	$230.3239	$230.32	$230.30	$230.30
Purchase #2	$103.79	9.856%	$114.0195	$114.02	$114.00	$114.00
Purchase #3	$85.42	4.420%	$89.1956	$89.20	$89.20	$89.20
Purchase #4	$139.54	7.754%	$150.3599	$150.36	$150.35	$150.40
Purchase #5	$137.28	10.429%	$151.5969	$151.60	$151.60	$151.60
Purchase #6	$191.66	9.625%	$210.1073	$210.11	$210.10	$210.10
Purchase #7	$202.90	9.632%	$222.4433	$222.44	$222.45	$222.40
7 purchase totals =	$1,064.95		$1,168.0464	$1,168.05	$1,168.00	$1,168.00