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	$225.91	5.777%	$238.9608	$238.96	$238.95	$239.00
Purchase #2	$131.95	11.521%	$147.152	$147.15	$147.15	$147.20
Purchase #3	$169.28	6.243%	$179.8482	$179.85	$179.85	$179.80
Purchase #4	$25.62	3.803%	$26.5943	$26.59	$26.60	$26.60
Purchase #5	$82.28	8.558%	$89.3215	$89.32	$89.30	$89.30
Purchase #6	$40.89	13.413%	$46.3746	$46.37	$46.35	$46.40
Purchase #7	$185.66	11.144%	$206.35	$206.35	$206.35	$206.40
7 purchase totals =	$861.59		$934.6014	$934.59	$934.55	$934.70