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	$186.83	6.630%	$199.2168	$199.22	$199.20	$199.20
Purchase #2	$174.49	8.694%	$189.6602	$189.66	$189.65	$189.70
Purchase #3	$223.89	3.214%	$231.0858	$231.09	$231.10	$231.10
Purchase #4	$230.87	5.729%	$244.0965	$244.10	$244.10	$244.10
Purchase #5	$203.59	7.435%	$218.7269	$218.73	$218.75	$218.70
Purchase #6	$103.96	7.567%	$111.8267	$111.83	$111.85	$111.80
Purchase #7	$82.78	8.611%	$89.9082	$89.91	$89.90	$89.90
7 purchase totals =	$1,206.41		$1,284.5211	$1,284.54	$1,284.55	$1,284.50