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	$85.95	5.460%	$90.6429	$90.64	$90.65	$90.60
Purchase #2	$28.70	5.144%	$30.1763	$30.18	$30.20	$30.20
Purchase #3	$85.73	3.196%	$88.4699	$88.47	$88.45	$88.50
Purchase #4	$138.86	3.722%	$144.0284	$144.03	$144.05	$144.00
Purchase #5	$84.89	4.294%	$88.5352	$88.54	$88.55	$88.50
Purchase #6	$120.51	7.582%	$129.6471	$129.65	$129.65	$129.60
Purchase #7	$50.58	13.861%	$57.5909	$57.59	$57.60	$57.60
7 purchase totals =	$595.22		$629.0907	$629.10	$629.15	$629.00