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	$130.87	8.739%	$142.3067	$142.31	$142.30	$142.30
Purchase #2	$105.54	6.498%	$112.398	$112.40	$112.40	$112.40
Purchase #3	$141.59	13.568%	$160.8009	$160.80	$160.80	$160.80
Purchase #4	$71.61	9.491%	$78.4065	$78.41	$78.40	$78.40
Purchase #5	$250.85	5.791%	$265.3767	$265.38	$265.40	$265.40
Purchase #6	$61.99	6.125%	$65.7869	$65.79	$65.80	$65.80
Purchase #7	$114.66	3.410%	$118.5699	$118.57	$118.55	$118.60
7 purchase totals =	$877.11		$943.6456	$943.66	$943.65	$943.70