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	$83.80	7.517%	$90.0992	$90.10	$90.10	$90.10
Purchase #2	$51.76	9.202%	$56.523	$56.52	$56.50	$56.50
Purchase #3	$50.85	7.253%	$54.5382	$54.54	$54.55	$54.50
Purchase #4	$96.68	8.667%	$105.0593	$105.06	$105.05	$105.10
Purchase #5	$200.59	3.799%	$208.2104	$208.21	$208.20	$208.20
Purchase #6	$82.95	7.139%	$88.8718	$88.87	$88.85	$88.90
Purchase #7	$147.45	4.471%	$154.0425	$154.04	$154.05	$154.00
7 purchase totals =	$714.08		$757.3444	$757.34	$757.30	$757.30