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	$36.95	7.630%	$39.7693	$39.77	$39.75	$39.80
Purchase #2	$113.77	11.630%	$127.0015	$127.00	$127.00	$127.00
Purchase #3	$133.39	3.341%	$137.8466	$137.85	$137.85	$137.80
Purchase #4	$211.71	11.513%	$236.0842	$236.08	$236.10	$236.10
Purchase #5	$144.73	8.866%	$157.5618	$157.56	$157.55	$157.60
Purchase #6	$89.83	11.146%	$99.8425	$99.84	$99.85	$99.80
Purchase #7	$112.35	13.649%	$127.6847	$127.68	$127.70	$127.70
7 purchase totals =	$842.73		$925.7906	$925.78	$925.80	$925.80