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	$96.91	3.530%	$100.3309	$100.33	$100.35	$100.30
Purchase #2	$138.59	7.430%	$148.8872	$148.89	$148.90	$148.90
Purchase #3	$28.69	9.434%	$31.3966	$31.40	$31.40	$31.40
Purchase #4	$141.80	8.822%	$154.3096	$154.31	$154.30	$154.30
Purchase #5	$66.53	6.532%	$70.8757	$70.88	$70.90	$70.90
Purchase #6	$127.92	13.632%	$145.3581	$145.36	$145.35	$145.40
Purchase #7	$144.53	8.355%	$156.6055	$156.61	$156.60	$156.60
7 purchase totals =	$744.97		$807.7636	$807.78	$807.80	$807.80