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	$236.67	3.699%	$245.4244	$245.42	$245.40	$245.40
Purchase #2	$111.66	5.216%	$117.4842	$117.48	$117.50	$117.50
Purchase #3	$143.90	8.326%	$155.8811	$155.88	$155.90	$155.90
Purchase #4	$128.37	3.828%	$133.284	$133.28	$133.30	$133.30
Purchase #5	$34.79	8.341%	$37.6918	$37.69	$37.70	$37.70
Purchase #6	$128.31	11.188%	$142.6653	$142.67	$142.65	$142.70
Purchase #7	$16.53	12.435%	$18.5855	$18.59	$18.60	$18.60
7 purchase totals =	$800.23		$851.0163	$851.01	$851.05	$851.10