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	$241.59	3.506%	$250.0601	$250.06	$250.05	$250.10
Purchase #2	$26.70	6.456%	$28.4238	$28.42	$28.40	$28.40
Purchase #3	$200.86	11.803%	$224.5675	$224.57	$224.55	$224.60
Purchase #4	$35.26	6.123%	$37.419	$37.42	$37.40	$37.40
Purchase #5	$133.54	9.725%	$146.5268	$146.53	$146.55	$146.50
Purchase #6	$24.64	6.836%	$26.3244	$26.32	$26.30	$26.30
Purchase #7	$118.31	4.793%	$123.9806	$123.98	$124.00	$124.00
7 purchase totals =	$780.90		$837.3022	$837.30	$837.25	$837.30