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	$6.77	11.606%	$7.5557	$7.56	$7.55	$7.60
Purchase #2	$32.28	10.134%	$35.5513	$35.55	$35.55	$35.60
Purchase #3	$173.66	5.334%	$182.923	$182.92	$182.90	$182.90
Purchase #4	$116.83	10.648%	$129.2701	$129.27	$129.25	$129.30
Purchase #5	$114.62	7.846%	$123.6131	$123.61	$123.60	$123.60
Purchase #6	$25.86	9.404%	$28.2919	$28.29	$28.30	$28.30
Purchase #7	$115.26	5.435%	$121.5244	$121.52	$121.50	$121.50
7 purchase totals =	$585.28		$628.7295	$628.72	$628.65	$628.80