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	$204.41	6.120%	$216.9199	$216.92	$216.90	$216.90
Purchase #2	$5.53	13.676%	$6.2863	$6.29	$6.30	$6.30
Purchase #3	$12.56	3.295%	$12.9739	$12.97	$12.95	$13.00
Purchase #4	$237.88	7.402%	$255.4879	$255.49	$255.50	$255.50
Purchase #5	$155.64	6.298%	$165.4422	$165.44	$165.45	$165.40
Purchase #6	$12.66	3.740%	$13.1335	$13.13	$13.15	$13.10
Purchase #7	$94.34	6.176%	$100.1664	$100.17	$100.15	$100.20
7 purchase totals =	$723.02		$770.4101	$770.41	$770.40	$770.40