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	$83.50	6.610%	$89.0194	$89.02	$89.00	$89.00
Purchase #2	$192.66	3.607%	$199.6092	$199.61	$199.60	$199.60
Purchase #3	$168.54	13.173%	$190.7418	$190.74	$190.75	$190.70
Purchase #4	$89.97	7.453%	$96.6755	$96.68	$96.70	$96.70
Purchase #5	$76.93	13.786%	$87.5356	$87.54	$87.55	$87.50
Purchase #6	$152.42	8.279%	$165.0389	$165.04	$165.05	$165.00
Purchase #7	$131.85	10.589%	$145.8116	$145.81	$145.80	$145.80
7 purchase totals =	$895.87		$974.4320	$974.44	$974.45	$974.30