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	$143.41	8.447%	$155.5238	$155.52	$155.50	$155.50
Purchase #2	$250.46	13.589%	$284.495	$284.50	$284.50	$284.50
Purchase #3	$167.39	4.480%	$174.8891	$174.89	$174.90	$174.90
Purchase #4	$79.69	13.749%	$90.6466	$90.65	$90.65	$90.60
Purchase #5	$248.96	13.109%	$281.5962	$281.60	$281.60	$281.60
Purchase #6	$115.56	8.702%	$125.616	$125.62	$125.60	$125.60
Purchase #7	$63.89	12.653%	$71.974	$71.97	$71.95	$72.00
7 purchase totals =	$1,069.36		$1,184.7407	$1,184.75	$1,184.70	$1,184.70