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	$27.90	3.573%	$28.8969	$28.90	$28.90	$28.90
Purchase #2	$123.52	8.130%	$133.5622	$133.56	$133.55	$133.60
Purchase #3	$118.86	10.649%	$131.5174	$131.52	$131.50	$131.50
Purchase #4	$183.44	8.498%	$199.0287	$199.03	$199.05	$199.00
Purchase #5	$6.27	6.332%	$6.667	$6.67	$6.65	$6.70
Purchase #6	$100.98	8.778%	$109.844	$109.84	$109.85	$109.80
Purchase #7	$35.62	5.613%	$37.6194	$37.62	$37.60	$37.60
7 purchase totals =	$596.59		$647.1356	$647.14	$647.10	$647.10