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	$241.94	7.386%	$259.8097	$259.81	$259.80	$259.80
Purchase #2	$103.38	12.619%	$116.4255	$116.43	$116.45	$116.40
Purchase #3	$175.27	9.678%	$192.2326	$192.23	$192.25	$192.20
Purchase #4	$73.47	13.443%	$83.3466	$83.35	$83.35	$83.30
Purchase #5	$147.61	3.532%	$152.8236	$152.82	$152.80	$152.80
Purchase #6	$96.66	11.851%	$108.1152	$108.12	$108.10	$108.10
Purchase #7	$244.57	13.872%	$278.4968	$278.50	$278.50	$278.50
7 purchase totals =	$1,082.90		$1,191.2500	$1,191.26	$1,191.25	$1,191.10