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	$55.42	11.494%	$61.79	$61.79	$61.80	$61.80
Purchase #2	$145.72	6.691%	$155.4701	$155.47	$155.45	$155.50
Purchase #3	$245.98	5.121%	$258.5766	$258.58	$258.60	$258.60
Purchase #4	$37.30	6.535%	$39.7376	$39.74	$39.75	$39.70
Purchase #5	$40.71	4.244%	$42.4377	$42.44	$42.45	$42.40
Purchase #6	$191.84	10.678%	$212.3247	$212.32	$212.30	$212.30
Purchase #7	$146.77	12.820%	$165.5859	$165.59	$165.60	$165.60
7 purchase totals =	$863.74		$935.9226	$935.93	$935.95	$935.90