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	$156.76	8.740%	$170.4608	$170.46	$170.45	$170.50
Purchase #2	$200.99	6.477%	$214.0081	$214.01	$214.00	$214.00
Purchase #3	$7.45	3.669%	$7.7233	$7.72	$7.70	$7.70
Purchase #4	$21.25	5.713%	$22.464	$22.46	$22.45	$22.50
Purchase #5	$102.31	6.332%	$108.7883	$108.79	$108.80	$108.80
Purchase #6	$38.69	10.756%	$42.8515	$42.85	$42.85	$42.90
Purchase #7	$83.88	7.640%	$90.2884	$90.29	$90.30	$90.30
7 purchase totals =	$611.33		$656.5844	$656.58	$656.55	$656.70