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	$164.54	9.642%	$180.4049	$180.40	$180.40	$180.40
Purchase #2	$10.90	9.580%	$11.9442	$11.94	$11.95	$11.90
Purchase #3	$171.61	8.154%	$185.6031	$185.60	$185.60	$185.60
Purchase #4	$137.72	8.792%	$149.8283	$149.83	$149.85	$149.80
Purchase #5	$149.44	7.289%	$160.3327	$160.33	$160.35	$160.30
Purchase #6	$143.40	13.146%	$162.2514	$162.25	$162.25	$162.30
Purchase #7	$123.49	6.237%	$131.1921	$131.19	$131.20	$131.20
7 purchase totals =	$901.10		$981.5567	$981.54	$981.60	$981.50