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	$112.88	9.398%	$123.4885	$123.49	$123.50	$123.50
Purchase #2	$99.37	8.163%	$107.4816	$107.48	$107.50	$107.50
Purchase #3	$71.25	13.365%	$80.7726	$80.77	$80.75	$80.80
Purchase #4	$144.37	8.680%	$156.9013	$156.90	$156.90	$156.90
Purchase #5	$146.33	3.253%	$151.0901	$151.09	$151.10	$151.10
Purchase #6	$130.29	9.519%	$142.6923	$142.69	$142.70	$142.70
Purchase #7	$158.90	12.547%	$178.8372	$178.84	$178.85	$178.80
7 purchase totals =	$863.39		$941.2636	$941.26	$941.30	$941.30