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	$29.37	4.451%	$30.6773	$30.68	$30.70	$30.70
Purchase #2	$165.66	10.155%	$182.4828	$182.48	$182.50	$182.50
Purchase #3	$80.96	12.259%	$90.8849	$90.88	$90.90	$90.90
Purchase #4	$110.35	11.506%	$123.0469	$123.05	$123.05	$123.00
Purchase #5	$41.54	10.129%	$45.7476	$45.75	$45.75	$45.70
Purchase #6	$59.91	11.246%	$66.6475	$66.65	$66.65	$66.60
Purchase #7	$231.35	7.635%	$249.0136	$249.01	$249.00	$249.00
7 purchase totals =	$719.14		$788.5006	$788.50	$788.55	$788.40