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	$44.83	10.447%	$49.5134	$49.51	$49.50	$49.50
Purchase #2	$86.43	7.369%	$92.799	$92.80	$92.80	$92.80
Purchase #3	$101.38	10.511%	$112.0361	$112.04	$112.05	$112.00
Purchase #4	$101.87	10.569%	$112.6366	$112.64	$112.65	$112.60
Purchase #5	$104.28	5.221%	$109.7245	$109.72	$109.70	$109.70
Purchase #6	$146.67	10.800%	$162.5104	$162.51	$162.50	$162.50
Purchase #7	$155.76	13.469%	$176.7393	$176.74	$176.75	$176.70
7 purchase totals =	$741.22		$815.9593	$815.96	$815.95	$815.80