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	$34.43	9.727%	$37.779	$37.78	$37.80	$37.80
Purchase #2	$141.50	6.781%	$151.0951	$151.10	$151.10	$151.10
Purchase #3	$142.28	10.788%	$157.6292	$157.63	$157.65	$157.60
Purchase #4	$45.33	11.319%	$50.4609	$50.46	$50.45	$50.50
Purchase #5	$173.42	5.723%	$183.3448	$183.34	$183.35	$183.30
Purchase #6	$81.47	12.123%	$91.3466	$91.35	$91.35	$91.30
Purchase #7	$143.25	9.504%	$156.8645	$156.86	$156.85	$156.90
7 purchase totals =	$761.68		$828.5201	$828.52	$828.55	$828.50