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	$36.42	4.642%	$38.1106	$38.11	$38.10	$38.10
Purchase #2	$215.64	11.565%	$240.5788	$240.58	$240.60	$240.60
Purchase #3	$72.64	11.385%	$80.9101	$80.91	$80.90	$80.90
Purchase #4	$131.69	11.142%	$146.3629	$146.36	$146.35	$146.40
Purchase #5	$32.82	9.619%	$35.977	$35.98	$36.00	$36.00
Purchase #6	$135.42	5.856%	$143.3502	$143.35	$143.35	$143.40
Purchase #7	$62.61	7.660%	$67.4059	$67.41	$67.40	$67.40
7 purchase totals =	$687.24		$752.6955	$752.70	$752.70	$752.80