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	$77.90	4.136%	$81.1219	$81.12	$81.10	$81.10
Purchase #2	$40.92	3.668%	$42.4209	$42.42	$42.40	$42.40
Purchase #3	$80.64	9.266%	$88.1121	$88.11	$88.10	$88.10
Purchase #4	$231.97	5.595%	$244.9487	$244.95	$244.95	$244.90
Purchase #5	$191.96	13.763%	$218.3795	$218.38	$218.40	$218.40
Purchase #6	$136.50	10.113%	$150.3042	$150.30	$150.30	$150.30
Purchase #7	$249.96	11.196%	$277.9455	$277.95	$277.95	$277.90
7 purchase totals =	$1,009.85		$1,103.2328	$1,103.23	$1,103.20	$1,103.10