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	$39.99	5.629%	$42.241	$42.24	$42.25	$42.20
Purchase #2	$187.37	4.344%	$195.5094	$195.51	$195.50	$195.50
Purchase #3	$174.52	9.309%	$190.7661	$190.77	$190.75	$190.80
Purchase #4	$118.80	8.133%	$128.462	$128.46	$128.45	$128.50
Purchase #5	$167.55	10.755%	$185.57	$185.57	$185.55	$185.60
Purchase #6	$47.77	6.420%	$50.8368	$50.84	$50.85	$50.80
Purchase #7	$109.39	13.233%	$123.8656	$123.87	$123.85	$123.90
7 purchase totals =	$845.39		$917.2509	$917.26	$917.20	$917.30