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	$83.98	8.210%	$90.8748	$90.87	$90.85	$90.90
Purchase #2	$207.51	7.207%	$222.4652	$222.47	$222.45	$222.50
Purchase #3	$40.32	7.524%	$43.3537	$43.35	$43.35	$43.40
Purchase #4	$27.66	5.645%	$29.2214	$29.22	$29.20	$29.20
Purchase #5	$35.37	3.222%	$36.5096	$36.51	$36.50	$36.50
Purchase #6	$188.43	12.701%	$212.3625	$212.36	$212.35	$212.40
Purchase #7	$25.25	10.865%	$27.9934	$27.99	$28.00	$28.00
7 purchase totals =	$608.52		$662.7806	$662.77	$662.70	$662.90