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	$142.42	4.678%	$149.0824	$149.08	$149.10	$149.10
Purchase #2	$164.40	12.164%	$184.3976	$184.40	$184.40	$184.40
Purchase #3	$165.35	3.465%	$171.0794	$171.08	$171.10	$171.10
Purchase #4	$197.76	12.524%	$222.5275	$222.53	$222.55	$222.50
Purchase #5	$17.39	10.245%	$19.1716	$19.17	$19.15	$19.20
Purchase #6	$90.60	9.817%	$99.4942	$99.49	$99.50	$99.50
Purchase #7	$225.78	8.201%	$244.2962	$244.30	$244.30	$244.30
7 purchase totals =	$1,003.70		$1,090.0489	$1,090.05	$1,090.10	$1,090.10