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	$159.61	3.274%	$164.8356	$164.84	$164.85	$164.80
Purchase #2	$223.54	7.445%	$240.1826	$240.18	$240.20	$240.20
Purchase #3	$56.55	6.577%	$60.2693	$60.27	$60.25	$60.30
Purchase #4	$218.64	9.112%	$238.5625	$238.56	$238.55	$238.60
Purchase #5	$155.69	10.187%	$171.5501	$171.55	$171.55	$171.60
Purchase #6	$139.44	7.871%	$150.4153	$150.42	$150.40	$150.40
Purchase #7	$240.93	5.874%	$255.0822	$255.08	$255.10	$255.10
7 purchase totals =	$1,194.40		$1,280.8976	$1,280.90	$1,280.90	$1,281.00