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	$153.65	9.346%	$168.0101	$168.01	$168.00	$168.00
Purchase #2	$154.34	8.378%	$167.2706	$167.27	$167.25	$167.30
Purchase #3	$29.79	4.721%	$31.1964	$31.20	$31.20	$31.20
Purchase #4	$189.41	11.849%	$211.8532	$211.85	$211.85	$211.90
Purchase #5	$123.76	3.635%	$128.2587	$128.26	$128.25	$128.30
Purchase #6	$159.62	11.755%	$178.3833	$178.38	$178.40	$178.40
Purchase #7	$56.85	4.621%	$59.477	$59.48	$59.50	$59.50
7 purchase totals =	$867.42		$944.4493	$944.45	$944.45	$944.60