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	$90.71	10.403%	$100.1466	$100.15	$100.15	$100.10
Purchase #2	$77.75	6.372%	$82.7042	$82.70	$82.70	$82.70
Purchase #3	$123.49	11.275%	$137.4135	$137.41	$137.40	$137.40
Purchase #4	$158.29	6.227%	$168.1467	$168.15	$168.15	$168.10
Purchase #5	$75.88	13.798%	$86.3499	$86.35	$86.35	$86.30
Purchase #6	$108.79	8.660%	$118.2112	$118.21	$118.20	$118.20
Purchase #7	$93.42	10.244%	$102.9899	$102.99	$103.00	$103.00
7 purchase totals =	$728.33		$795.9620	$795.96	$795.95	$795.80