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	$74.27	5.700%	$78.5034	$78.50	$78.50	$78.50
Purchase #2	$160.89	3.833%	$167.0569	$167.06	$167.05	$167.10
Purchase #3	$25.46	9.287%	$27.8245	$27.82	$27.80	$27.80
Purchase #4	$102.40	4.145%	$106.6445	$106.64	$106.65	$106.60
Purchase #5	$201.74	7.494%	$216.8584	$216.86	$216.85	$216.90
Purchase #6	$143.33	10.150%	$157.878	$157.88	$157.90	$157.90
Purchase #7	$53.62	7.516%	$57.6501	$57.65	$57.65	$57.70
7 purchase totals =	$761.71		$812.4158	$812.41	$812.40	$812.50