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	$225.94	7.501%	$242.8878	$242.89	$242.90	$242.90
Purchase #2	$117.25	9.668%	$128.5857	$128.59	$128.60	$128.60
Purchase #3	$180.27	11.129%	$200.3322	$200.33	$200.35	$200.30
Purchase #4	$45.73	9.490%	$50.0698	$50.07	$50.05	$50.10
Purchase #5	$136.60	5.662%	$144.3343	$144.33	$144.35	$144.30
Purchase #6	$96.34	11.871%	$107.7765	$107.78	$107.80	$107.80
Purchase #7	$48.76	3.401%	$50.4183	$50.42	$50.40	$50.40
7 purchase totals =	$850.89		$924.4046	$924.41	$924.45	$924.40