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	$97.41	3.299%	$100.6236	$100.62	$100.60	$100.60
Purchase #2	$162.90	7.275%	$174.751	$174.75	$174.75	$174.80
Purchase #3	$90.44	7.738%	$97.4382	$97.44	$97.45	$97.40
Purchase #4	$29.45	4.826%	$30.8713	$30.87	$30.85	$30.90
Purchase #5	$130.43	9.134%	$142.3435	$142.34	$142.35	$142.30
Purchase #6	$163.84	13.478%	$185.9224	$185.92	$185.90	$185.90
Purchase #7	$99.81	9.670%	$109.4616	$109.46	$109.45	$109.50
7 purchase totals =	$774.28		$841.4116	$841.40	$841.35	$841.40