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	$183.82	9.124%	$200.5917	$200.59	$200.60	$200.60
Purchase #2	$161.63	10.311%	$178.2957	$178.30	$178.30	$178.30
Purchase #3	$209.40	10.740%	$231.8896	$231.89	$231.90	$231.90
Purchase #4	$160.55	8.797%	$174.6736	$174.67	$174.65	$174.70
Purchase #5	$49.43	10.169%	$54.4565	$54.46	$54.45	$54.50
Purchase #6	$96.46	5.470%	$101.7364	$101.74	$101.75	$101.70
Purchase #7	$35.73	7.223%	$38.3108	$38.31	$38.30	$38.30
7 purchase totals =	$897.02		$979.9543	$979.96	$979.95	$980.00