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	$240.62	13.710%	$273.609	$273.61	$273.60	$273.60
Purchase #2	$174.26	3.824%	$180.9237	$180.92	$180.90	$180.90
Purchase #3	$126.41	5.716%	$133.6356	$133.64	$133.65	$133.60
Purchase #4	$97.40	12.413%	$109.4903	$109.49	$109.50	$109.50
Purchase #5	$127.73	3.716%	$132.4764	$132.48	$132.50	$132.50
Purchase #6	$167.26	9.611%	$183.3354	$183.34	$183.35	$183.30
Purchase #7	$85.74	4.789%	$89.8461	$89.85	$89.85	$89.80
7 purchase totals =	$1,019.42		$1,103.3165	$1,103.33	$1,103.35	$1,103.20