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	$12.73	7.713%	$13.7119	$13.71	$13.70	$13.70
Purchase #2	$17.92	13.134%	$20.2736	$20.27	$20.25	$20.30
Purchase #3	$75.32	4.410%	$78.6416	$78.64	$78.65	$78.60
Purchase #4	$196.77	13.265%	$222.8715	$222.87	$222.85	$222.90
Purchase #5	$175.48	3.364%	$181.3831	$181.38	$181.40	$181.40
Purchase #6	$180.63	12.654%	$203.4869	$203.49	$203.50	$203.50
Purchase #7	$60.55	4.826%	$63.4721	$63.47	$63.45	$63.50
7 purchase totals =	$719.40		$783.8407	$783.83	$783.80	$783.90