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	$73.25	11.296%	$81.5243	$81.52	$81.50	$81.50
Purchase #2	$174.38	4.820%	$182.7851	$182.79	$182.80	$182.80
Purchase #3	$89.90	12.681%	$101.3002	$101.30	$101.30	$101.30
Purchase #4	$82.72	9.177%	$90.3112	$90.31	$90.30	$90.30
Purchase #5	$228.79	8.228%	$247.6148	$247.61	$247.60	$247.60
Purchase #6	$68.75	12.618%	$77.4249	$77.42	$77.40	$77.40
Purchase #7	$14.56	5.427%	$15.3502	$15.35	$15.35	$15.40
7 purchase totals =	$732.35		$796.3107	$796.30	$796.25	$796.30