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	$64.72	10.639%	$71.6056	$71.61	$71.60	$71.60
Purchase #2	$99.57	3.105%	$102.6616	$102.66	$102.65	$102.70
Purchase #3	$249.26	12.698%	$280.911	$280.91	$280.90	$280.90
Purchase #4	$174.70	4.182%	$182.006	$182.01	$182.00	$182.00
Purchase #5	$137.79	6.428%	$146.6471	$146.65	$146.65	$146.60
Purchase #6	$33.88	11.701%	$37.8443	$37.84	$37.85	$37.80
Purchase #7	$43.62	9.645%	$47.8271	$47.83	$47.85	$47.80
7 purchase totals =	$803.54		$869.5027	$869.51	$869.50	$869.40