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	$74.92	7.113%	$80.2491	$80.25	$80.25	$80.20
Purchase #2	$106.37	6.757%	$113.5574	$113.56	$113.55	$113.60
Purchase #3	$135.27	6.222%	$143.6865	$143.69	$143.70	$143.70
Purchase #4	$237.61	13.789%	$270.374	$270.37	$270.35	$270.40
Purchase #5	$52.79	13.361%	$59.8433	$59.84	$59.85	$59.80
Purchase #6	$20.36	5.149%	$21.4083	$21.41	$21.40	$21.40
Purchase #7	$136.61	13.372%	$154.8775	$154.88	$154.90	$154.90
7 purchase totals =	$763.93		$843.9961	$844.00	$844.00	$844.00