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	$151.73	4.219%	$158.1315	$158.13	$158.15	$158.10
Purchase #2	$39.68	13.740%	$45.132	$45.13	$45.15	$45.10
Purchase #3	$111.73	12.342%	$125.5197	$125.52	$125.50	$125.50
Purchase #4	$164.67	9.180%	$179.7867	$179.79	$179.80	$179.80
Purchase #5	$182.60	7.292%	$195.9152	$195.92	$195.90	$195.90
Purchase #6	$124.59	13.833%	$141.8245	$141.82	$141.80	$141.80
Purchase #7	$134.64	8.309%	$145.8272	$145.83	$145.85	$145.80
7 purchase totals =	$909.64		$992.1368	$992.14	$992.15	$992.00