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	$160.85	5.166%	$169.1595	$169.16	$169.15	$169.20
Purchase #2	$38.37	9.826%	$42.1402	$42.14	$42.15	$42.10
Purchase #3	$188.45	5.236%	$198.3172	$198.32	$198.30	$198.30
Purchase #4	$112.72	13.210%	$127.6103	$127.61	$127.60	$127.60
Purchase #5	$120.38	9.194%	$131.4477	$131.45	$131.45	$131.40
Purchase #6	$148.51	8.271%	$160.7933	$160.79	$160.80	$160.80
Purchase #7	$40.91	9.869%	$44.9474	$44.95	$44.95	$44.90
7 purchase totals =	$810.19		$874.4156	$874.42	$874.40	$874.30