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	$51.94	11.810%	$58.0741	$58.07	$58.05	$58.10
Purchase #2	$241.48	7.415%	$259.3857	$259.39	$259.40	$259.40
Purchase #3	$127.75	4.731%	$133.7939	$133.79	$133.80	$133.80
Purchase #4	$129.78	11.651%	$144.9007	$144.90	$144.90	$144.90
Purchase #5	$98.55	3.360%	$101.8613	$101.86	$101.85	$101.90
Purchase #6	$38.30	6.111%	$40.6405	$40.64	$40.65	$40.60
Purchase #7	$64.81	12.415%	$72.8562	$72.86	$72.85	$72.90
7 purchase totals =	$752.61		$811.5124	$811.51	$811.50	$811.60