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	$31.57	3.868%	$32.7911	$32.79	$32.80	$32.80
Purchase #2	$98.81	6.403%	$105.1368	$105.14	$105.15	$105.10
Purchase #3	$236.33	3.494%	$244.5874	$244.59	$244.60	$244.60
Purchase #4	$103.47	3.707%	$107.3056	$107.31	$107.30	$107.30
Purchase #5	$47.78	8.485%	$51.8341	$51.83	$51.85	$51.80
Purchase #6	$57.27	4.340%	$59.7555	$59.76	$59.75	$59.80
Purchase #7	$185.82	12.377%	$208.8189	$208.82	$208.80	$208.80
7 purchase totals =	$761.05		$810.2294	$810.24	$810.25	$810.20