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	$121.38	5.848%	$128.4783	$128.48	$128.50	$128.50
Purchase #2	$202.60	13.448%	$229.8456	$229.85	$229.85	$229.80
Purchase #3	$167.65	9.104%	$182.9129	$182.91	$182.90	$182.90
Purchase #4	$54.32	13.317%	$61.5538	$61.55	$61.55	$61.60
Purchase #5	$43.64	9.684%	$47.8661	$47.87	$47.85	$47.90
Purchase #6	$139.48	7.105%	$149.3901	$149.39	$149.40	$149.40
Purchase #7	$228.62	13.658%	$259.8449	$259.84	$259.85	$259.80
7 purchase totals =	$957.69		$1,059.8917	$1,059.89	$1,059.90	$1,059.90