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	$7.76	3.614%	$8.0404	$8.04	$8.05	$8.00
Purchase #2	$96.99	13.328%	$109.9168	$109.92	$109.90	$109.90
Purchase #3	$152.35	3.402%	$157.5329	$157.53	$157.55	$157.50
Purchase #4	$249.72	12.712%	$281.4644	$281.46	$281.45	$281.50
Purchase #5	$47.55	12.752%	$53.6136	$53.61	$53.60	$53.60
Purchase #6	$82.46	11.693%	$92.102	$92.10	$92.10	$92.10
Purchase #7	$127.65	8.567%	$138.5858	$138.59	$138.60	$138.60
7 purchase totals =	$764.48		$841.2559	$841.25	$841.25	$841.20