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	$38.79	9.528%	$42.4859	$42.49	$42.50	$42.50
Purchase #2	$66.36	7.661%	$71.4438	$71.44	$71.45	$71.40
Purchase #3	$28.47	3.808%	$29.5541	$29.55	$29.55	$29.60
Purchase #4	$243.89	11.485%	$271.9008	$271.90	$271.90	$271.90
Purchase #5	$95.57	9.680%	$104.8212	$104.82	$104.80	$104.80
Purchase #6	$143.75	9.422%	$157.2941	$157.29	$157.30	$157.30
Purchase #7	$70.54	4.292%	$73.5676	$73.57	$73.55	$73.60
7 purchase totals =	$687.37		$751.0675	$751.06	$751.05	$751.10