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	$157.62	3.363%	$162.9208	$162.92	$162.90	$162.90
Purchase #2	$95.43	5.186%	$100.379	$100.38	$100.40	$100.40
Purchase #3	$209.37	8.373%	$226.9006	$226.90	$226.90	$226.90
Purchase #4	$9.84	5.815%	$10.4122	$10.41	$10.40	$10.40
Purchase #5	$73.77	6.562%	$78.6108	$78.61	$78.60	$78.60
Purchase #6	$94.32	9.118%	$102.9201	$102.92	$102.90	$102.90
Purchase #7	$122.75	10.818%	$136.0291	$136.03	$136.05	$136.00
7 purchase totals =	$763.10		$818.1726	$818.17	$818.15	$818.10