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	$51.82	10.173%	$57.0916	$57.09	$57.10	$57.10
Purchase #2	$174.81	7.826%	$188.4906	$188.49	$188.50	$188.50
Purchase #3	$37.95	7.792%	$40.9071	$40.91	$40.90	$40.90
Purchase #4	$125.25	9.712%	$137.4143	$137.41	$137.40	$137.40
Purchase #5	$116.80	9.293%	$127.6542	$127.65	$127.65	$127.70
Purchase #6	$67.73	3.544%	$70.1304	$70.13	$70.15	$70.10
Purchase #7	$66.35	13.693%	$75.4353	$75.44	$75.45	$75.40
7 purchase totals =	$640.71		$697.1235	$697.12	$697.15	$697.10