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	$231.54	3.464%	$239.5605	$239.56	$239.55	$239.60
Purchase #2	$42.89	12.141%	$48.0973	$48.10	$48.10	$48.10
Purchase #3	$180.66	8.840%	$196.6303	$196.63	$196.65	$196.60
Purchase #4	$50.55	9.334%	$55.2683	$55.27	$55.25	$55.30
Purchase #5	$211.95	4.775%	$222.0706	$222.07	$222.05	$222.10
Purchase #6	$171.86	7.873%	$185.3905	$185.39	$185.40	$185.40
Purchase #7	$144.30	12.816%	$162.7935	$162.79	$162.80	$162.80
7 purchase totals =	$1,033.75		$1,109.8110	$1,109.81	$1,109.80	$1,109.90