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	$170.50	7.108%	$182.6191	$182.62	$182.60	$182.60
Purchase #2	$135.87	4.223%	$141.6078	$141.61	$141.60	$141.60
Purchase #3	$118.35	7.463%	$127.1825	$127.18	$127.20	$127.20
Purchase #4	$39.98	5.208%	$42.0622	$42.06	$42.05	$42.10
Purchase #5	$74.92	12.798%	$84.5083	$84.51	$84.50	$84.50
Purchase #6	$149.36	8.528%	$162.0974	$162.10	$162.10	$162.10
Purchase #7	$80.29	12.179%	$90.0685	$90.07	$90.05	$90.10
7 purchase totals =	$769.27		$830.1458	$830.15	$830.10	$830.20