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	$20.88	9.551%	$22.8742	$22.87	$22.85	$22.90
Purchase #2	$15.73	10.591%	$17.396	$17.40	$17.40	$17.40
Purchase #3	$70.80	10.605%	$78.3083	$78.31	$78.30	$78.30
Purchase #4	$83.28	6.326%	$88.5483	$88.55	$88.55	$88.50
Purchase #5	$28.72	9.524%	$31.4553	$31.46	$31.45	$31.50
Purchase #6	$47.97	13.776%	$54.5783	$54.58	$54.60	$54.60
Purchase #7	$189.84	13.556%	$215.5747	$215.57	$215.55	$215.60
7 purchase totals =	$457.22		$508.7351	$508.74	$508.70	$508.80