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	$50.25	12.583%	$56.573	$56.57	$56.55	$56.60
Purchase #2	$189.96	3.516%	$196.639	$196.64	$196.65	$196.60
Purchase #3	$40.55	7.498%	$43.5904	$43.59	$43.60	$43.60
Purchase #4	$92.33	9.479%	$101.082	$101.08	$101.10	$101.10
Purchase #5	$102.89	7.595%	$110.7045	$110.70	$110.70	$110.70
Purchase #6	$230.41	11.472%	$256.8426	$256.84	$256.85	$256.80
Purchase #7	$158.38	10.214%	$174.5569	$174.56	$174.55	$174.60
7 purchase totals =	$864.77		$939.9884	$939.98	$940.00	$940.00