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	$32.79	8.260%	$35.4985	$35.50	$35.50	$35.50
Purchase #2	$36.40	11.326%	$40.5227	$40.52	$40.50	$40.50
Purchase #3	$200.47	8.308%	$217.125	$217.13	$217.15	$217.10
Purchase #4	$118.55	9.144%	$129.3902	$129.39	$129.40	$129.40
Purchase #5	$85.27	6.342%	$90.6778	$90.68	$90.70	$90.70
Purchase #6	$64.89	10.685%	$71.8235	$71.82	$71.80	$71.80
Purchase #7	$104.27	8.867%	$113.5156	$113.52	$113.50	$113.50
7 purchase totals =	$642.64		$698.5533	$698.56	$698.55	$698.50