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	$52.85	8.459%	$57.3206	$57.32	$57.30	$57.30
Purchase #2	$83.42	7.408%	$89.5998	$89.60	$89.60	$89.60
Purchase #3	$147.76	3.260%	$152.577	$152.58	$152.60	$152.60
Purchase #4	$148.26	13.124%	$167.7176	$167.72	$167.70	$167.70
Purchase #5	$29.70	13.287%	$33.6462	$33.65	$33.65	$33.60
Purchase #6	$178.28	10.238%	$196.5323	$196.53	$196.55	$196.50
Purchase #7	$165.57	10.794%	$183.4416	$183.44	$183.45	$183.40
7 purchase totals =	$805.84		$880.8351	$880.84	$880.85	$880.70