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	$14.29	10.166%	$15.7427	$15.74	$15.75	$15.70
Purchase #2	$249.51	8.779%	$271.4145	$271.41	$271.40	$271.40
Purchase #3	$173.76	8.638%	$188.7694	$188.77	$188.75	$188.80
Purchase #4	$41.37	4.303%	$43.1502	$43.15	$43.15	$43.20
Purchase #5	$243.51	4.734%	$255.0378	$255.04	$255.05	$255.00
Purchase #6	$98.71	12.839%	$111.3834	$111.38	$111.40	$111.40
Purchase #7	$196.62	5.396%	$207.2296	$207.23	$207.25	$207.20
7 purchase totals =	$1,017.77		$1,092.7276	$1,092.72	$1,092.75	$1,092.70