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	$155.54	5.540%	$164.1569	$164.16	$164.15	$164.20
Purchase #2	$87.99	13.593%	$99.9505	$99.95	$99.95	$100.00
Purchase #3	$234.35	3.662%	$242.9319	$242.93	$242.95	$242.90
Purchase #4	$69.31	13.231%	$78.4804	$78.48	$78.50	$78.50
Purchase #5	$38.92	6.214%	$41.3385	$41.34	$41.35	$41.30
Purchase #6	$112.94	3.783%	$117.2125	$117.21	$117.20	$117.20
Purchase #7	$35.95	5.125%	$37.7924	$37.79	$37.80	$37.80
7 purchase totals =	$735.00		$781.8631	$781.86	$781.90	$781.90