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	$105.26	12.221%	$118.1238	$118.12	$118.10	$118.10
Purchase #2	$160.76	7.822%	$173.3346	$173.33	$173.35	$173.30
Purchase #3	$167.50	12.285%	$188.0774	$188.08	$188.10	$188.10
Purchase #4	$101.26	3.860%	$105.1686	$105.17	$105.15	$105.20
Purchase #5	$50.52	10.762%	$55.957	$55.96	$55.95	$56.00
Purchase #6	$98.90	6.146%	$104.9784	$104.98	$105.00	$105.00
Purchase #7	$35.25	7.705%	$37.966	$37.97	$37.95	$38.00
7 purchase totals =	$719.45		$783.6058	$783.61	$783.60	$783.70