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	$130.29	8.514%	$141.3829	$141.38	$141.40	$141.40
Purchase #2	$98.92	11.608%	$110.4026	$110.40	$110.40	$110.40
Purchase #3	$41.79	9.547%	$45.7797	$45.78	$45.80	$45.80
Purchase #4	$128.66	12.401%	$144.6151	$144.62	$144.60	$144.60
Purchase #5	$143.94	11.434%	$160.3981	$160.40	$160.40	$160.40
Purchase #6	$62.97	11.425%	$70.1643	$70.16	$70.15	$70.20
Purchase #7	$131.86	7.868%	$142.2347	$142.23	$142.25	$142.20
7 purchase totals =	$738.43		$814.9774	$814.97	$815.00	$815.00