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	$29.46	7.300%	$31.6106	$31.61	$31.60	$31.60
Purchase #2	$85.37	11.639%	$95.3062	$95.31	$95.30	$95.30
Purchase #3	$137.39	5.259%	$144.6153	$144.62	$144.60	$144.60
Purchase #4	$86.53	4.222%	$90.1833	$90.18	$90.20	$90.20
Purchase #5	$201.55	13.143%	$228.0397	$228.04	$228.05	$228.00
Purchase #6	$117.72	7.813%	$126.9175	$126.92	$126.90	$126.90
Purchase #7	$159.96	3.347%	$165.3139	$165.31	$165.30	$165.30
7 purchase totals =	$817.98		$881.9865	$881.99	$881.95	$881.90