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	$54.37	10.208%	$59.9201	$59.92	$59.90	$59.90
Purchase #2	$113.59	12.281%	$127.54	$127.54	$127.55	$127.50
Purchase #3	$110.36	4.334%	$115.143	$115.14	$115.15	$115.10
Purchase #4	$78.84	6.477%	$83.9465	$83.95	$83.95	$83.90
Purchase #5	$143.67	4.273%	$149.809	$149.81	$149.80	$149.80
Purchase #6	$159.85	8.808%	$173.9296	$173.93	$173.95	$173.90
Purchase #7	$59.91	10.265%	$66.0598	$66.06	$66.05	$66.10
7 purchase totals =	$720.59		$776.3480	$776.35	$776.35	$776.20