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	$174.91	8.175%	$189.2089	$189.21	$189.20	$189.20
Purchase #2	$179.46	11.690%	$200.4389	$200.44	$200.45	$200.40
Purchase #3	$248.56	12.637%	$279.9705	$279.97	$279.95	$280.00
Purchase #4	$182.91	5.445%	$192.8694	$192.87	$192.85	$192.90
Purchase #5	$86.91	4.262%	$90.6141	$90.61	$90.60	$90.60
Purchase #6	$185.89	4.786%	$194.7867	$194.79	$194.80	$194.80
Purchase #7	$167.51	13.233%	$189.6766	$189.68	$189.70	$189.70
7 purchase totals =	$1,226.15		$1,337.5651	$1,337.57	$1,337.55	$1,337.60