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	$17.40	4.160%	$18.1238	$18.12	$18.10	$18.10
Purchase #2	$235.55	9.683%	$258.3583	$258.36	$258.35	$258.40
Purchase #3	$124.77	5.244%	$131.3129	$131.31	$131.30	$131.30
Purchase #4	$53.61	6.637%	$57.1681	$57.17	$57.15	$57.20
Purchase #5	$234.94	11.472%	$261.8923	$261.89	$261.90	$261.90
Purchase #6	$66.98	6.705%	$71.471	$71.47	$71.45	$71.50
Purchase #7	$166.72	12.636%	$187.7867	$187.79	$187.80	$187.80
7 purchase totals =	$899.97		$986.1131	$986.11	$986.05	$986.20