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	$28.80	5.838%	$30.4813	$30.48	$30.50	$30.50
Purchase #2	$180.95	8.632%	$196.5696	$196.57	$196.55	$196.60
Purchase #3	$53.78	5.237%	$56.5965	$56.60	$56.60	$56.60
Purchase #4	$59.45	4.860%	$62.3393	$62.34	$62.35	$62.30
Purchase #5	$125.39	8.691%	$136.2876	$136.29	$136.30	$136.30
Purchase #6	$227.90	13.826%	$259.4095	$259.41	$259.40	$259.40
Purchase #7	$206.31	13.633%	$234.4362	$234.44	$234.45	$234.40
7 purchase totals =	$882.58		$976.1200	$976.13	$976.15	$976.10