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	$126.30	12.763%	$142.4197	$142.42	$142.40	$142.40
Purchase #2	$168.43	3.640%	$174.5609	$174.56	$174.55	$174.60
Purchase #3	$111.92	3.533%	$115.8741	$115.87	$115.85	$115.90
Purchase #4	$145.66	3.593%	$150.8936	$150.89	$150.90	$150.90
Purchase #5	$36.52	9.553%	$40.0088	$40.01	$40.00	$40.00
Purchase #6	$123.30	6.814%	$131.7017	$131.70	$131.70	$131.70
Purchase #7	$62.27	5.853%	$65.9147	$65.91	$65.90	$65.90
7 purchase totals =	$774.40		$821.3735	$821.36	$821.30	$821.40