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	$25.65	8.683%	$27.8772	$27.88	$27.90	$27.90
Purchase #2	$187.86	6.375%	$199.8361	$199.84	$199.85	$199.80
Purchase #3	$16.55	12.836%	$18.6744	$18.67	$18.65	$18.70
Purchase #4	$122.63	8.117%	$132.5839	$132.58	$132.60	$132.60
Purchase #5	$127.68	10.463%	$141.0392	$141.04	$141.05	$141.00
Purchase #6	$53.77	10.654%	$59.4987	$59.50	$59.50	$59.50
Purchase #7	$140.59	8.374%	$152.363	$152.36	$152.35	$152.40
7 purchase totals =	$674.73		$731.8725	$731.87	$731.90	$731.90