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	$9.78	4.109%	$10.1819	$10.18	$10.20	$10.20
Purchase #2	$142.31	12.385%	$159.9351	$159.94	$159.95	$159.90
Purchase #3	$165.59	11.475%	$184.5915	$184.59	$184.60	$184.60
Purchase #4	$136.90	4.747%	$143.3986	$143.40	$143.40	$143.40
Purchase #5	$194.74	12.407%	$218.9014	$218.90	$218.90	$218.90
Purchase #6	$191.86	8.837%	$208.8147	$208.81	$208.80	$208.80
Purchase #7	$152.97	9.642%	$167.7194	$167.72	$167.70	$167.70
7 purchase totals =	$994.15		$1,093.5426	$1,093.54	$1,093.55	$1,093.50