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	$62.67	13.608%	$71.1981	$71.20	$71.20	$71.20
Purchase #2	$171.72	8.163%	$185.7375	$185.74	$185.75	$185.70
Purchase #3	$43.38	10.784%	$48.0581	$48.06	$48.05	$48.10
Purchase #4	$71.51	12.675%	$80.5739	$80.57	$80.55	$80.60
Purchase #5	$53.43	7.698%	$57.543	$57.54	$57.55	$57.50
Purchase #6	$231.69	3.816%	$240.5313	$240.53	$240.55	$240.50
Purchase #7	$191.87	3.148%	$197.9101	$197.91	$197.90	$197.90
7 purchase totals =	$826.27		$881.5520	$881.55	$881.55	$881.50