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	$54.83	12.550%	$61.7112	$61.71	$61.70	$61.70
Purchase #2	$91.45	12.772%	$103.13	$103.13	$103.15	$103.10
Purchase #3	$53.39	11.295%	$59.4204	$59.42	$59.40	$59.40
Purchase #4	$247.95	3.728%	$257.1936	$257.19	$257.20	$257.20
Purchase #5	$166.59	4.466%	$174.0299	$174.03	$174.05	$174.00
Purchase #6	$125.54	6.238%	$133.3712	$133.37	$133.35	$133.40
Purchase #7	$59.78	9.415%	$65.4083	$65.41	$65.40	$65.40
7 purchase totals =	$799.53		$854.2646	$854.26	$854.25	$854.20