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	$18.25	13.804%	$20.7692	$20.77	$20.75	$20.80
Purchase #2	$164.43	10.144%	$181.1098	$181.11	$181.10	$181.10
Purchase #3	$94.37	6.272%	$100.2889	$100.29	$100.30	$100.30
Purchase #4	$133.56	5.134%	$140.417	$140.42	$140.40	$140.40
Purchase #5	$170.60	13.287%	$193.2676	$193.27	$193.25	$193.30
Purchase #6	$130.32	9.258%	$142.385	$142.39	$142.40	$142.40
Purchase #7	$186.86	13.129%	$211.3928	$211.39	$211.40	$211.40
7 purchase totals =	$898.39		$989.6303	$989.64	$989.60	$989.70