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	$124.63	6.584%	$132.8356	$132.84	$132.85	$132.80
Purchase #2	$34.45	3.285%	$35.5817	$35.58	$35.60	$35.60
Purchase #3	$89.78	9.165%	$98.0083	$98.01	$98.00	$98.00
Purchase #4	$66.75	9.372%	$73.0058	$73.01	$73.00	$73.00
Purchase #5	$204.56	8.285%	$221.5078	$221.51	$221.50	$221.50
Purchase #6	$83.51	8.708%	$90.7821	$90.78	$90.80	$90.80
Purchase #7	$129.96	9.590%	$142.4232	$142.42	$142.40	$142.40
7 purchase totals =	$733.64		$794.1445	$794.15	$794.15	$794.10