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	$100.43	11.118%	$111.5958	$111.60	$111.60	$111.60
Purchase #2	$134.69	11.661%	$150.3962	$150.40	$150.40	$150.40
Purchase #3	$55.46	3.368%	$57.3279	$57.33	$57.35	$57.30
Purchase #4	$201.45	9.155%	$219.8927	$219.89	$219.90	$219.90
Purchase #5	$72.26	11.363%	$80.4709	$80.47	$80.45	$80.50
Purchase #6	$121.45	7.131%	$130.1106	$130.11	$130.10	$130.10
Purchase #7	$86.89	5.588%	$91.7454	$91.75	$91.75	$91.70
7 purchase totals =	$772.63		$841.5395	$841.55	$841.55	$841.50