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	$28.42	11.568%	$31.7076	$31.71	$31.70	$31.70
Purchase #2	$222.72	4.303%	$232.3036	$232.30	$232.30	$232.30
Purchase #3	$217.38	6.445%	$231.3901	$231.39	$231.40	$231.40
Purchase #4	$164.54	8.711%	$178.8731	$178.87	$178.85	$178.90
Purchase #5	$62.53	4.667%	$65.4483	$65.45	$65.45	$65.40
Purchase #6	$250.60	5.398%	$264.1274	$264.13	$264.15	$264.10
Purchase #7	$161.37	3.821%	$167.5359	$167.54	$167.55	$167.50
7 purchase totals =	$1,107.56		$1,171.3860	$1,171.39	$1,171.40	$1,171.30