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	$147.71	8.281%	$159.9419	$159.94	$159.95	$159.90
Purchase #2	$58.55	7.468%	$62.9225	$62.92	$62.90	$62.90
Purchase #3	$162.27	13.257%	$183.7821	$183.78	$183.80	$183.80
Purchase #4	$91.46	7.597%	$98.4082	$98.41	$98.40	$98.40
Purchase #5	$99.78	4.303%	$104.0735	$104.07	$104.05	$104.10
Purchase #6	$139.67	3.423%	$144.4509	$144.45	$144.45	$144.50
Purchase #7	$111.45	5.194%	$117.2387	$117.24	$117.25	$117.20
7 purchase totals =	$810.89		$870.8178	$870.81	$870.80	$870.80