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	$204.90	9.161%	$223.6709	$223.67	$223.65	$223.70
Purchase #2	$68.97	5.716%	$72.9123	$72.91	$72.90	$72.90
Purchase #3	$237.75	5.303%	$250.3579	$250.36	$250.35	$250.40
Purchase #4	$128.69	12.247%	$144.4507	$144.45	$144.45	$144.50
Purchase #5	$40.30	5.537%	$42.5314	$42.53	$42.55	$42.50
Purchase #6	$79.65	7.669%	$85.7584	$85.76	$85.75	$85.80
Purchase #7	$95.99	7.610%	$103.2948	$103.29	$103.30	$103.30
7 purchase totals =	$856.25		$922.9764	$922.97	$922.95	$923.10