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	$91.58	9.323%	$100.118	$100.12	$100.10	$100.10
Purchase #2	$115.60	7.240%	$123.9694	$123.97	$123.95	$124.00
Purchase #3	$114.80	8.787%	$124.8875	$124.89	$124.90	$124.90
Purchase #4	$176.47	10.477%	$194.9588	$194.96	$194.95	$195.00
Purchase #5	$109.84	4.594%	$114.886	$114.89	$114.90	$114.90
Purchase #6	$25.90	5.118%	$27.2256	$27.23	$27.25	$27.20
Purchase #7	$54.74	13.113%	$61.9181	$61.92	$61.90	$61.90
7 purchase totals =	$688.93		$747.9634	$747.98	$747.95	$748.00