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	$168.59	5.777%	$178.3294	$178.33	$178.35	$178.30
Purchase #2	$57.62	11.242%	$64.0976	$64.10	$64.10	$64.10
Purchase #3	$121.44	7.477%	$130.5201	$130.52	$130.50	$130.50
Purchase #4	$72.69	13.236%	$82.3112	$82.31	$82.30	$82.30
Purchase #5	$229.70	3.425%	$237.5672	$237.57	$237.55	$237.60
Purchase #6	$137.62	4.252%	$143.4716	$143.47	$143.45	$143.50
Purchase #7	$171.73	7.639%	$184.8485	$184.85	$184.85	$184.80
7 purchase totals =	$959.39		$1,021.1456	$1,021.15	$1,021.10	$1,021.10