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	$158.29	6.427%	$168.4633	$168.46	$168.45	$168.50
Purchase #2	$129.53	3.315%	$133.8239	$133.82	$133.80	$133.80
Purchase #3	$50.60	11.397%	$56.3669	$56.37	$56.35	$56.40
Purchase #4	$26.68	7.868%	$28.7792	$28.78	$28.80	$28.80
Purchase #5	$241.98	13.172%	$273.8536	$273.85	$273.85	$273.90
Purchase #6	$228.67	7.829%	$246.5726	$246.57	$246.55	$246.60
Purchase #7	$82.97	10.283%	$91.5018	$91.50	$91.50	$91.50
7 purchase totals =	$918.72		$999.3613	$999.35	$999.30	$999.50