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	$7.57	6.641%	$8.0727	$8.07	$8.05	$8.10
Purchase #2	$161.60	6.784%	$172.5629	$172.56	$172.55	$172.60
Purchase #3	$167.72	12.235%	$188.2405	$188.24	$188.25	$188.20
Purchase #4	$135.94	7.352%	$145.9343	$145.93	$145.95	$145.90
Purchase #5	$34.31	9.155%	$37.4511	$37.45	$37.45	$37.50
Purchase #6	$246.76	9.659%	$270.5945	$270.59	$270.60	$270.60
Purchase #7	$230.60	12.243%	$258.8324	$258.83	$258.85	$258.80
7 purchase totals =	$984.50		$1,081.6884	$1,081.67	$1,081.70	$1,081.70