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	$40.47	4.833%	$42.4259	$42.43	$42.45	$42.40
Purchase #2	$75.44	10.507%	$83.3665	$83.37	$83.35	$83.40
Purchase #3	$120.61	11.358%	$134.3089	$134.31	$134.30	$134.30
Purchase #4	$15.50	9.841%	$17.0254	$17.03	$17.05	$17.00
Purchase #5	$179.78	6.486%	$191.4405	$191.44	$191.45	$191.40
Purchase #6	$49.31	13.582%	$56.0073	$56.01	$56.00	$56.00
Purchase #7	$87.59	4.801%	$91.7952	$91.80	$91.80	$91.80
7 purchase totals =	$568.70		$616.3697	$616.39	$616.40	$616.30