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	$34.51	10.309%	$38.0676	$38.07	$38.05	$38.10
Purchase #2	$165.27	12.362%	$185.7007	$185.70	$185.70	$185.70
Purchase #3	$42.76	11.244%	$47.5679	$47.57	$47.55	$47.60
Purchase #4	$119.42	10.555%	$132.0248	$132.02	$132.00	$132.00
Purchase #5	$74.93	11.860%	$83.8167	$83.82	$83.80	$83.80
Purchase #6	$79.89	4.772%	$83.7024	$83.70	$83.70	$83.70
Purchase #7	$79.55	12.873%	$89.7905	$89.79	$89.80	$89.80
7 purchase totals =	$596.33		$660.6706	$660.67	$660.60	$660.70