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	$218.74	10.740%	$242.2327	$242.23	$242.25	$242.20
Purchase #2	$129.62	12.748%	$146.144	$146.14	$146.15	$146.10
Purchase #3	$96.82	3.311%	$100.0257	$100.03	$100.05	$100.00
Purchase #4	$139.71	8.831%	$152.0478	$152.05	$152.05	$152.00
Purchase #5	$167.87	4.677%	$175.7213	$175.72	$175.70	$175.70
Purchase #6	$25.44	13.273%	$28.8167	$28.82	$28.80	$28.80
Purchase #7	$140.64	10.111%	$154.8601	$154.86	$154.85	$154.90
7 purchase totals =	$918.84		$999.8483	$999.85	$999.85	$999.70