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	$62.59	12.610%	$70.4826	$70.48	$70.50	$70.50
Purchase #2	$225.88	3.417%	$233.5983	$233.60	$233.60	$233.60
Purchase #3	$155.79	10.537%	$172.2056	$172.21	$172.20	$172.20
Purchase #4	$34.89	9.769%	$38.2984	$38.30	$38.30	$38.30
Purchase #5	$29.27	10.723%	$32.4086	$32.41	$32.40	$32.40
Purchase #6	$104.56	4.478%	$109.2422	$109.24	$109.25	$109.20
Purchase #7	$33.58	12.199%	$37.6764	$37.68	$37.70	$37.70
7 purchase totals =	$646.56		$693.9121	$693.92	$693.95	$693.90