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	$51.55	5.174%	$54.2172	$54.22	$54.20	$54.20
Purchase #2	$194.44	7.265%	$208.5661	$208.57	$208.55	$208.60
Purchase #3	$39.87	8.224%	$43.1489	$43.15	$43.15	$43.10
Purchase #4	$60.72	9.295%	$66.3639	$66.36	$66.35	$66.40
Purchase #5	$35.56	7.197%	$38.1193	$38.12	$38.10	$38.10
Purchase #6	$215.60	3.844%	$223.8877	$223.89	$223.90	$223.90
Purchase #7	$136.79	12.829%	$154.3388	$154.34	$154.35	$154.30
7 purchase totals =	$734.53		$788.6419	$788.65	$788.60	$788.60