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	$10.42	11.301%	$11.5976	$11.60	$11.60	$11.60
Purchase #2	$115.85	9.479%	$126.8314	$126.83	$126.85	$126.80
Purchase #3	$88.49	12.491%	$99.5433	$99.54	$99.55	$99.50
Purchase #4	$225.89	12.859%	$254.9372	$254.94	$254.95	$254.90
Purchase #5	$216.65	7.638%	$233.1977	$233.20	$233.20	$233.20
Purchase #6	$185.91	12.732%	$209.5801	$209.58	$209.60	$209.60
Purchase #7	$40.26	11.372%	$44.8384	$44.84	$44.85	$44.80
7 purchase totals =	$883.47		$980.5257	$980.53	$980.60	$980.40