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	$5.51	13.700%	$6.2649	$6.26	$6.25	$6.30
Purchase #2	$41.73	11.536%	$46.544	$46.54	$46.55	$46.50
Purchase #3	$217.45	9.118%	$237.2771	$237.28	$237.30	$237.30
Purchase #4	$148.90	10.753%	$164.9112	$164.91	$164.90	$164.90
Purchase #5	$186.44	5.372%	$196.4556	$196.46	$196.45	$196.50
Purchase #6	$122.59	5.240%	$129.0137	$129.01	$129.00	$129.00
Purchase #7	$56.81	3.545%	$58.8239	$58.82	$58.80	$58.80
7 purchase totals =	$779.43		$839.2904	$839.28	$839.25	$839.30