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	$223.68	7.737%	$240.9861	$240.99	$241.00	$241.00
Purchase #2	$233.69	9.794%	$256.5776	$256.58	$256.60	$256.60
Purchase #3	$145.65	13.294%	$165.0127	$165.01	$165.00	$165.00
Purchase #4	$21.47	12.788%	$24.2156	$24.22	$24.20	$24.20
Purchase #5	$180.92	12.838%	$204.1465	$204.15	$204.15	$204.10
Purchase #6	$65.33	10.154%	$71.9636	$71.96	$71.95	$72.00
Purchase #7	$103.56	7.300%	$111.1199	$111.12	$111.10	$111.10
7 purchase totals =	$974.30		$1,074.0220	$1,074.03	$1,074.00	$1,074.00