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	$46.40	8.278%	$50.241	$50.24	$50.25	$50.20
Purchase #2	$48.72	12.811%	$54.9615	$54.96	$54.95	$55.00
Purchase #3	$80.61	10.856%	$89.361	$89.36	$89.35	$89.40
Purchase #4	$245.62	10.807%	$272.1642	$272.16	$272.15	$272.20
Purchase #5	$17.83	13.520%	$20.2406	$20.24	$20.25	$20.20
Purchase #6	$77.88	4.451%	$81.3464	$81.35	$81.35	$81.30
Purchase #7	$58.66	4.564%	$61.3372	$61.34	$61.35	$61.30
7 purchase totals =	$575.72		$629.6519	$629.65	$629.65	$629.60