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	$83.89	5.716%	$88.6852	$88.69	$88.70	$88.70
Purchase #2	$165.94	10.558%	$183.4599	$183.46	$183.45	$183.50
Purchase #3	$17.91	9.556%	$19.6215	$19.62	$19.60	$19.60
Purchase #4	$160.61	6.666%	$171.3163	$171.32	$171.30	$171.30
Purchase #5	$50.36	9.163%	$54.9745	$54.97	$54.95	$55.00
Purchase #6	$21.96	8.708%	$23.8723	$23.87	$23.85	$23.90
Purchase #7	$85.79	4.370%	$89.539	$89.54	$89.55	$89.50
7 purchase totals =	$586.46		$631.4687	$631.47	$631.40	$631.50