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	$135.78	3.507%	$140.5418	$140.54	$140.55	$140.50
Purchase #2	$136.91	5.779%	$144.822	$144.82	$144.80	$144.80
Purchase #3	$68.60	9.367%	$75.0258	$75.03	$75.05	$75.00
Purchase #4	$94.25	4.378%	$98.3763	$98.38	$98.40	$98.40
Purchase #5	$91.67	11.242%	$101.9755	$101.98	$102.00	$102.00
Purchase #6	$38.50	4.367%	$40.1813	$40.18	$40.20	$40.20
Purchase #7	$55.32	8.231%	$59.8734	$59.87	$59.85	$59.90
7 purchase totals =	$621.03		$660.7961	$660.80	$660.85	$660.80