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	$210.62	8.435%	$228.3858	$228.39	$228.40	$228.40
Purchase #2	$40.67	12.673%	$45.8241	$45.82	$45.80	$45.80
Purchase #3	$112.72	10.462%	$124.5128	$124.51	$124.50	$124.50
Purchase #4	$89.53	11.659%	$99.9683	$99.97	$99.95	$100.00
Purchase #5	$130.30	12.784%	$146.9576	$146.96	$146.95	$147.00
Purchase #6	$95.34	3.326%	$98.511	$98.51	$98.50	$98.50
Purchase #7	$169.40	10.170%	$186.628	$186.63	$186.65	$186.60
7 purchase totals =	$848.58		$930.7876	$930.79	$930.75	$930.80