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	$184.48	3.570%	$191.0659	$191.07	$191.05	$191.10
Purchase #2	$76.45	13.661%	$86.8938	$86.89	$86.90	$86.90
Purchase #3	$134.37	4.632%	$140.594	$140.59	$140.60	$140.60
Purchase #4	$38.83	6.426%	$41.3252	$41.33	$41.35	$41.30
Purchase #5	$91.90	4.117%	$95.6835	$95.68	$95.70	$95.70
Purchase #6	$39.88	4.255%	$41.5769	$41.58	$41.60	$41.60
Purchase #7	$75.86	9.222%	$82.8558	$82.86	$82.85	$82.90
7 purchase totals =	$641.77		$679.9951	$680.00	$680.05	$680.10