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	$199.31	9.223%	$217.6924	$217.69	$217.70	$217.70
Purchase #2	$173.62	6.122%	$184.249	$184.25	$184.25	$184.20
Purchase #3	$116.93	6.155%	$124.127	$124.13	$124.15	$124.10
Purchase #4	$18.81	13.359%	$21.3228	$21.32	$21.30	$21.30
Purchase #5	$128.97	12.623%	$145.2499	$145.25	$145.25	$145.20
Purchase #6	$84.83	6.157%	$90.053	$90.05	$90.05	$90.10
Purchase #7	$29.69	11.846%	$33.2071	$33.21	$33.20	$33.20
7 purchase totals =	$752.16		$815.9012	$815.90	$815.90	$815.80