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	$6.40	3.240%	$6.6074	$6.61	$6.60	$6.60
Purchase #2	$114.61	9.466%	$125.459	$125.46	$125.45	$125.50
Purchase #3	$91.43	5.669%	$96.6132	$96.61	$96.60	$96.60
Purchase #4	$133.42	11.633%	$148.9407	$148.94	$148.95	$148.90
Purchase #5	$57.96	5.630%	$61.2231	$61.22	$61.20	$61.20
Purchase #6	$246.50	5.794%	$260.7822	$260.78	$260.80	$260.80
Purchase #7	$72.60	13.390%	$82.3211	$82.32	$82.30	$82.30
7 purchase totals =	$722.92		$781.9467	$781.94	$781.90	$781.90