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	$159.51	4.164%	$166.152	$166.15	$166.15	$166.20
Purchase #2	$6.85	8.638%	$7.4417	$7.44	$7.45	$7.40
Purchase #3	$160.72	6.685%	$171.4641	$171.46	$171.45	$171.50
Purchase #4	$170.54	5.533%	$179.976	$179.98	$180.00	$180.00
Purchase #5	$39.46	10.229%	$43.4964	$43.50	$43.50	$43.50
Purchase #6	$248.35	6.851%	$265.3645	$265.36	$265.35	$265.40
Purchase #7	$72.59	4.379%	$75.7687	$75.77	$75.75	$75.80
7 purchase totals =	$858.02		$909.6634	$909.66	$909.65	$909.80