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	$77.28	6.125%	$82.0134	$82.01	$82.00	$82.00
Purchase #2	$133.71	7.665%	$143.9589	$143.96	$143.95	$144.00
Purchase #3	$73.39	9.240%	$80.1712	$80.17	$80.15	$80.20
Purchase #4	$214.56	12.752%	$241.9207	$241.92	$241.90	$241.90
Purchase #5	$32.79	3.469%	$33.9275	$33.93	$33.95	$33.90
Purchase #6	$31.66	3.334%	$32.7155	$32.72	$32.70	$32.70
Purchase #7	$74.89	6.456%	$79.7249	$79.72	$79.70	$79.70
7 purchase totals =	$638.28		$694.4321	$694.43	$694.35	$694.40