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	$66.27	3.380%	$68.5099	$68.51	$68.50	$68.50
Purchase #2	$123.99	10.320%	$136.7858	$136.79	$136.80	$136.80
Purchase #3	$30.60	13.654%	$34.7781	$34.78	$34.80	$34.80
Purchase #4	$57.39	3.808%	$59.5754	$59.58	$59.60	$59.60
Purchase #5	$92.27	7.534%	$99.2216	$99.22	$99.20	$99.20
Purchase #6	$214.83	3.158%	$221.6143	$221.61	$221.60	$221.60
Purchase #7	$250.34	6.410%	$266.3868	$266.39	$266.40	$266.40
7 purchase totals =	$835.69		$886.8719	$886.88	$886.90	$886.90