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	$85.41	6.274%	$90.7686	$90.77	$90.75	$90.80
Purchase #2	$178.98	11.354%	$199.3014	$199.30	$199.30	$199.30
Purchase #3	$100.37	6.359%	$106.7525	$106.75	$106.75	$106.80
Purchase #4	$46.51	4.849%	$48.7653	$48.77	$48.75	$48.80
Purchase #5	$201.63	11.725%	$225.2711	$225.27	$225.25	$225.30
Purchase #6	$130.71	12.826%	$147.4749	$147.47	$147.45	$147.50
Purchase #7	$154.25	8.223%	$166.934	$166.93	$166.95	$166.90
7 purchase totals =	$897.86		$985.2678	$985.26	$985.20	$985.40