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	$188.57	4.224%	$196.5352	$196.54	$196.55	$196.50
Purchase #2	$44.61	8.586%	$48.4402	$48.44	$48.45	$48.40
Purchase #3	$232.71	10.665%	$257.5285	$257.53	$257.55	$257.50
Purchase #4	$207.96	7.639%	$223.8461	$223.85	$223.85	$223.80
Purchase #5	$39.59	6.478%	$42.1546	$42.15	$42.15	$42.20
Purchase #6	$129.27	13.513%	$146.7383	$146.74	$146.75	$146.70
Purchase #7	$134.83	6.379%	$143.4308	$143.43	$143.45	$143.40
7 purchase totals =	$977.54		$1,058.6737	$1,058.68	$1,058.75	$1,058.50