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	$72.63	8.292%	$78.6525	$78.65	$78.65	$78.70
Purchase #2	$21.28	10.638%	$23.5438	$23.54	$23.55	$23.50
Purchase #3	$166.93	8.537%	$181.1808	$181.18	$181.20	$181.20
Purchase #4	$109.53	12.414%	$123.1271	$123.13	$123.15	$123.10
Purchase #5	$35.40	13.707%	$40.2523	$40.25	$40.25	$40.30
Purchase #6	$61.73	9.422%	$67.5462	$67.55	$67.55	$67.50
Purchase #7	$142.65	4.653%	$149.2875	$149.29	$149.30	$149.30
7 purchase totals =	$610.15		$663.5902	$663.59	$663.65	$663.60