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	$75.92	6.594%	$80.9262	$80.93	$80.95	$80.90
Purchase #2	$34.35	3.397%	$35.5169	$35.52	$35.50	$35.50
Purchase #3	$62.98	8.453%	$68.3037	$68.30	$68.30	$68.30
Purchase #4	$137.25	3.320%	$141.8067	$141.81	$141.80	$141.80
Purchase #5	$73.31	13.874%	$83.481	$83.48	$83.50	$83.50
Purchase #6	$42.72	6.151%	$45.3477	$45.35	$45.35	$45.30
Purchase #7	$16.71	12.288%	$18.7633	$18.76	$18.75	$18.80
7 purchase totals =	$443.24		$474.1455	$474.15	$474.15	$474.10