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	$99.34	12.695%	$111.9512	$111.95	$111.95	$112.00
Purchase #2	$42.77	3.283%	$44.1741	$44.17	$44.15	$44.20
Purchase #3	$39.90	12.528%	$44.8987	$44.90	$44.90	$44.90
Purchase #4	$145.39	13.754%	$165.3869	$165.39	$165.40	$165.40
Purchase #5	$164.41	9.113%	$179.3927	$179.39	$179.40	$179.40
Purchase #6	$223.88	10.286%	$246.9083	$246.91	$246.90	$246.90
Purchase #7	$50.69	5.444%	$53.4496	$53.45	$53.45	$53.40
7 purchase totals =	$766.38		$846.1615	$846.16	$846.15	$846.20