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	$93.69	6.124%	$99.4276	$99.43	$99.45	$99.40
Purchase #2	$89.52	7.161%	$95.9305	$95.93	$95.95	$95.90
Purchase #3	$90.67	7.250%	$97.2436	$97.24	$97.25	$97.20
Purchase #4	$19.96	8.439%	$21.6444	$21.64	$21.65	$21.60
Purchase #5	$52.97	4.283%	$55.2387	$55.24	$55.25	$55.20
Purchase #6	$244.81	8.753%	$266.2382	$266.24	$266.25	$266.20
Purchase #7	$105.60	6.618%	$112.5886	$112.59	$112.60	$112.60
7 purchase totals =	$697.22		$748.3116	$748.31	$748.40	$748.10