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	$6.79	13.279%	$7.6916	$7.69	$7.70	$7.70
Purchase #2	$155.97	7.380%	$167.4806	$167.48	$167.50	$167.50
Purchase #3	$40.83	5.711%	$43.1618	$43.16	$43.15	$43.20
Purchase #4	$72.84	5.113%	$76.5643	$76.56	$76.55	$76.60
Purchase #5	$126.74	5.813%	$134.1074	$134.11	$134.10	$134.10
Purchase #6	$89.39	12.185%	$100.2822	$100.28	$100.30	$100.30
Purchase #7	$81.79	13.546%	$92.8693	$92.87	$92.85	$92.90
7 purchase totals =	$574.35		$622.1572	$622.15	$622.15	$622.30