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	$144.43	5.383%	$152.2047	$152.20	$152.20	$152.20
Purchase #2	$215.52	10.625%	$238.419	$238.42	$238.40	$238.40
Purchase #3	$191.26	10.849%	$212.0098	$212.01	$212.00	$212.00
Purchase #4	$166.81	6.399%	$177.4842	$177.48	$177.50	$177.50
Purchase #5	$130.70	9.703%	$143.3818	$143.38	$143.40	$143.40
Purchase #6	$177.99	10.150%	$196.056	$196.06	$196.05	$196.10
Purchase #7	$167.69	7.845%	$180.8453	$180.85	$180.85	$180.80
7 purchase totals =	$1,194.40		$1,300.4008	$1,300.40	$1,300.40	$1,300.40