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	$175.90	12.777%	$198.3747	$198.37	$198.35	$198.40
Purchase #2	$145.88	5.411%	$153.7736	$153.77	$153.75	$153.80
Purchase #3	$219.25	11.228%	$243.8674	$243.87	$243.85	$243.90
Purchase #4	$99.45	11.592%	$110.9782	$110.98	$111.00	$111.00
Purchase #5	$50.40	10.216%	$55.5489	$55.55	$55.55	$55.50
Purchase #6	$28.98	12.278%	$32.5382	$32.54	$32.55	$32.50
Purchase #7	$36.36	4.813%	$38.11	$38.11	$38.10	$38.10
7 purchase totals =	$756.22		$833.1910	$833.19	$833.15	$833.20