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	$155.56	12.151%	$174.4621	$174.46	$174.45	$174.50
Purchase #2	$50.47	3.334%	$52.1527	$52.15	$52.15	$52.20
Purchase #3	$79.98	11.351%	$89.0585	$89.06	$89.05	$89.10
Purchase #4	$11.58	12.277%	$13.0017	$13.00	$13.00	$13.00
Purchase #5	$194.51	5.205%	$204.6342	$204.63	$204.65	$204.60
Purchase #6	$81.33	3.116%	$83.8642	$83.86	$83.85	$83.90
Purchase #7	$89.53	9.755%	$98.2637	$98.26	$98.25	$98.30
7 purchase totals =	$662.96		$715.4371	$715.42	$715.40	$715.60