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	$73.77	6.778%	$78.7701	$78.77	$78.75	$78.80
Purchase #2	$154.60	10.813%	$171.3169	$171.32	$171.30	$171.30
Purchase #3	$69.70	5.476%	$73.5168	$73.52	$73.50	$73.50
Purchase #4	$51.80	10.825%	$57.4074	$57.41	$57.40	$57.40
Purchase #5	$248.62	7.354%	$266.9035	$266.90	$266.90	$266.90
Purchase #6	$136.75	13.231%	$154.8434	$154.84	$154.85	$154.80
Purchase #7	$41.42	9.491%	$45.3512	$45.35	$45.35	$45.40
7 purchase totals =	$776.66		$848.1093	$848.11	$848.05	$848.10