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	$157.39	13.142%	$178.0742	$178.07	$178.05	$178.10
Purchase #2	$179.55	5.183%	$188.8561	$188.86	$188.85	$188.90
Purchase #3	$106.65	8.715%	$115.9445	$115.94	$115.95	$115.90
Purchase #4	$185.52	8.288%	$200.8959	$200.90	$200.90	$200.90
Purchase #5	$233.28	6.863%	$249.29	$249.29	$249.30	$249.30
Purchase #6	$73.38	6.173%	$77.9097	$77.91	$77.90	$77.90
Purchase #7	$79.83	12.255%	$89.6132	$89.61	$89.60	$89.60
7 purchase totals =	$1,015.60		$1,100.5836	$1,100.58	$1,100.55	$1,100.60