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	$45.30	12.212%	$50.832	$50.83	$50.85	$50.80
Purchase #2	$201.89	11.822%	$225.7574	$225.76	$225.75	$225.80
Purchase #3	$115.54	10.777%	$127.9917	$127.99	$128.00	$128.00
Purchase #4	$175.65	12.365%	$197.3691	$197.37	$197.35	$197.40
Purchase #5	$223.72	13.290%	$253.4524	$253.45	$253.45	$253.50
Purchase #6	$38.77	10.312%	$42.768	$42.77	$42.75	$42.80
Purchase #7	$85.61	5.358%	$90.197	$90.20	$90.20	$90.20
7 purchase totals =	$886.48		$988.3676	$988.37	$988.35	$988.50