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	$71.99	9.524%	$78.8463	$78.85	$78.85	$78.80
Purchase #2	$201.95	4.740%	$211.5224	$211.52	$211.50	$211.50
Purchase #3	$72.37	11.141%	$80.4327	$80.43	$80.45	$80.40
Purchase #4	$159.39	5.425%	$168.0369	$168.04	$168.05	$168.00
Purchase #5	$36.31	6.795%	$38.7773	$38.78	$38.80	$38.80
Purchase #6	$150.68	11.346%	$167.7762	$167.78	$167.80	$167.80
Purchase #7	$215.70	6.194%	$229.0605	$229.06	$229.05	$229.10
7 purchase totals =	$908.39		$974.4523	$974.46	$974.50	$974.40