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	$206.51	13.754%	$234.9134	$234.91	$234.90	$234.90
Purchase #2	$115.69	12.287%	$129.9048	$129.90	$129.90	$129.90
Purchase #3	$56.99	8.113%	$61.6136	$61.61	$61.60	$61.60
Purchase #4	$18.61	13.313%	$21.0875	$21.09	$21.10	$21.10
Purchase #5	$147.76	9.653%	$162.0233	$162.02	$162.00	$162.00
Purchase #6	$181.50	10.258%	$200.1183	$200.12	$200.10	$200.10
Purchase #7	$103.61	7.643%	$111.5289	$111.53	$111.55	$111.50
7 purchase totals =	$830.67		$921.1898	$921.18	$921.15	$921.10