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	$65.60	12.450%	$73.7672	$73.77	$73.75	$73.80
Purchase #2	$232.72	3.673%	$241.2678	$241.27	$241.25	$241.30
Purchase #3	$102.25	7.829%	$110.2552	$110.26	$110.25	$110.30
Purchase #4	$89.98	7.163%	$96.4253	$96.43	$96.45	$96.40
Purchase #5	$129.45	12.697%	$145.8863	$145.89	$145.90	$145.90
Purchase #6	$75.43	10.820%	$83.5915	$83.59	$83.60	$83.60
Purchase #7	$99.93	4.301%	$104.228	$104.23	$104.25	$104.20
7 purchase totals =	$795.36		$855.4213	$855.44	$855.45	$855.50