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	$241.79	4.672%	$253.0864	$253.09	$253.10	$253.10
Purchase #2	$165.31	11.717%	$184.6794	$184.68	$184.70	$184.70
Purchase #3	$90.25	9.498%	$98.8219	$98.82	$98.80	$98.80
Purchase #4	$63.45	11.468%	$70.7264	$70.73	$70.75	$70.70
Purchase #5	$128.33	11.785%	$143.4537	$143.45	$143.45	$143.50
Purchase #6	$228.94	9.850%	$251.4906	$251.49	$251.50	$251.50
Purchase #7	$89.83	12.606%	$101.154	$101.15	$101.15	$101.20
7 purchase totals =	$1,007.90		$1,103.4124	$1,103.41	$1,103.45	$1,103.50