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	$242.89	12.550%	$273.3727	$273.37	$273.35	$273.40
Purchase #2	$246.38	4.222%	$256.7822	$256.78	$256.80	$256.80
Purchase #3	$204.77	8.709%	$222.6034	$222.60	$222.60	$222.60
Purchase #4	$144.48	5.312%	$152.1548	$152.15	$152.15	$152.20
Purchase #5	$75.86	9.821%	$83.3102	$83.31	$83.30	$83.30
Purchase #6	$240.92	7.197%	$258.259	$258.26	$258.25	$258.30
Purchase #7	$52.58	6.622%	$56.0618	$56.06	$56.05	$56.10
7 purchase totals =	$1,207.88		$1,302.5441	$1,302.53	$1,302.50	$1,302.70