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	$73.74	5.727%	$77.9631	$77.96	$77.95	$78.00
Purchase #2	$115.56	13.831%	$131.5431	$131.54	$131.55	$131.50
Purchase #3	$36.72	13.114%	$41.5355	$41.54	$41.55	$41.50
Purchase #4	$236.66	7.307%	$253.9527	$253.95	$253.95	$254.00
Purchase #5	$218.55	9.490%	$239.2904	$239.29	$239.30	$239.30
Purchase #6	$99.39	3.592%	$102.9601	$102.96	$102.95	$103.00
Purchase #7	$122.83	6.719%	$131.0829	$131.08	$131.10	$131.10
7 purchase totals =	$903.45		$978.3278	$978.32	$978.35	$978.40