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	$166.58	7.841%	$179.6415	$179.64	$179.65	$179.60
Purchase #2	$174.83	6.131%	$185.5488	$185.55	$185.55	$185.50
Purchase #3	$204.75	11.568%	$228.4355	$228.44	$228.45	$228.40
Purchase #4	$50.63	10.835%	$56.1158	$56.12	$56.10	$56.10
Purchase #5	$228.97	12.386%	$257.3302	$257.33	$257.35	$257.30
Purchase #6	$78.56	5.476%	$82.8619	$82.86	$82.85	$82.90
Purchase #7	$13.39	3.554%	$13.8659	$13.87	$13.85	$13.90
7 purchase totals =	$917.71		$1,003.7996	$1,003.81	$1,003.80	$1,003.70