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	$233.76	13.577%	$265.4976	$265.50	$265.50	$265.50
Purchase #2	$240.29	10.858%	$266.3807	$266.38	$266.40	$266.40
Purchase #3	$91.92	13.439%	$104.2731	$104.27	$104.25	$104.30
Purchase #4	$25.74	5.260%	$27.0939	$27.09	$27.10	$27.10
Purchase #5	$75.40	3.793%	$78.2599	$78.26	$78.25	$78.30
Purchase #6	$141.98	3.192%	$146.512	$146.51	$146.50	$146.50
Purchase #7	$57.58	5.744%	$60.8874	$60.89	$60.90	$60.90
7 purchase totals =	$866.67		$948.9046	$948.90	$948.90	$949.00