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	$83.36	4.864%	$87.4146	$87.41	$87.40	$87.40
Purchase #2	$51.97	3.321%	$53.6959	$53.70	$53.70	$53.70
Purchase #3	$81.83	10.360%	$90.3076	$90.31	$90.30	$90.30
Purchase #4	$140.89	10.232%	$155.3059	$155.31	$155.30	$155.30
Purchase #5	$188.94	13.600%	$214.6358	$214.64	$214.65	$214.60
Purchase #6	$209.50	9.337%	$229.061	$229.06	$229.05	$229.10
Purchase #7	$222.65	12.715%	$250.9599	$250.96	$250.95	$251.00
7 purchase totals =	$979.14		$1,081.3807	$1,081.39	$1,081.35	$1,081.40