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	$34.28	11.686%	$38.286	$38.29	$38.30	$38.30
Purchase #2	$198.74	8.487%	$215.6071	$215.61	$215.60	$215.60
Purchase #3	$209.79	4.686%	$219.6208	$219.62	$219.60	$219.60
Purchase #4	$180.77	13.865%	$205.8338	$205.83	$205.85	$205.80
Purchase #5	$191.64	12.522%	$215.6372	$215.64	$215.65	$215.60
Purchase #6	$199.46	6.641%	$212.7061	$212.71	$212.70	$212.70
Purchase #7	$51.64	9.586%	$56.5902	$56.59	$56.60	$56.60
7 purchase totals =	$1,066.32		$1,164.2812	$1,164.29	$1,164.30	$1,164.20