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	$119.65	7.519%	$128.6465	$128.65	$128.65	$128.60
Purchase #2	$100.64	8.220%	$108.9126	$108.91	$108.90	$108.90
Purchase #3	$81.35	4.514%	$85.0221	$85.02	$85.00	$85.00
Purchase #4	$149.43	6.372%	$158.9517	$158.95	$158.95	$159.00
Purchase #5	$81.45	8.385%	$88.2796	$88.28	$88.30	$88.30
Purchase #6	$111.78	4.278%	$116.5619	$116.56	$116.55	$116.60
Purchase #7	$134.52	3.662%	$139.4461	$139.45	$139.45	$139.40
7 purchase totals =	$778.82		$825.8205	$825.82	$825.80	$825.80