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	$70.79	9.769%	$77.7055	$77.71	$77.70	$77.70
Purchase #2	$31.41	4.842%	$32.9309	$32.93	$32.95	$32.90
Purchase #3	$42.87	6.793%	$45.7822	$45.78	$45.80	$45.80
Purchase #4	$45.48	4.158%	$47.3711	$47.37	$47.35	$47.40
Purchase #5	$19.83	5.120%	$20.8453	$20.85	$20.85	$20.80
Purchase #6	$163.72	12.137%	$183.5907	$183.59	$183.60	$183.60
Purchase #7	$38.67	7.591%	$41.6054	$41.61	$41.60	$41.60
7 purchase totals =	$412.77		$449.8311	$449.84	$449.85	$449.80