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	$81.51	7.623%	$87.7235	$87.72	$87.70	$87.70
Purchase #2	$116.36	13.379%	$131.9278	$131.93	$131.95	$131.90
Purchase #3	$101.48	9.548%	$111.1693	$111.17	$111.15	$111.20
Purchase #4	$26.41	9.118%	$28.8181	$28.82	$28.80	$28.80
Purchase #5	$148.27	13.793%	$168.7209	$168.72	$168.70	$168.70
Purchase #6	$99.52	7.712%	$107.195	$107.20	$107.20	$107.20
Purchase #7	$47.39	12.661%	$53.39	$53.39	$53.40	$53.40
7 purchase totals =	$620.94		$688.9446	$688.95	$688.90	$688.90