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	$76.93	3.798%	$79.8518	$79.85	$79.85	$79.90
Purchase #2	$140.87	4.648%	$147.4176	$147.42	$147.40	$147.40
Purchase #3	$133.46	12.810%	$150.5562	$150.56	$150.55	$150.60
Purchase #4	$54.86	5.599%	$57.9316	$57.93	$57.95	$57.90
Purchase #5	$134.72	9.360%	$147.3298	$147.33	$147.35	$147.30
Purchase #6	$114.33	3.605%	$118.4516	$118.45	$118.45	$118.50
Purchase #7	$208.40	5.242%	$219.3243	$219.32	$219.30	$219.30
7 purchase totals =	$863.57		$920.8629	$920.86	$920.85	$920.90