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	$204.52	11.794%	$228.6411	$228.64	$228.65	$228.60
Purchase #2	$128.84	6.164%	$136.7817	$136.78	$136.80	$136.80
Purchase #3	$52.63	12.360%	$59.1351	$59.14	$59.15	$59.10
Purchase #4	$32.50	3.284%	$33.5673	$33.57	$33.55	$33.60
Purchase #5	$187.98	12.613%	$211.6899	$211.69	$211.70	$211.70
Purchase #6	$143.96	11.737%	$160.8566	$160.86	$160.85	$160.90
Purchase #7	$44.46	9.645%	$48.7482	$48.75	$48.75	$48.70
7 purchase totals =	$794.89		$879.4199	$879.43	$879.45	$879.40