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	$37.36	12.428%	$42.0031	$42.00	$42.00	$42.00
Purchase #2	$167.39	4.360%	$174.6882	$174.69	$174.70	$174.70
Purchase #3	$137.93	5.520%	$145.5437	$145.54	$145.55	$145.50
Purchase #4	$167.37	11.456%	$186.5439	$186.54	$186.55	$186.50
Purchase #5	$111.81	12.129%	$125.3714	$125.37	$125.35	$125.40
Purchase #6	$186.87	6.437%	$198.8988	$198.90	$198.90	$198.90
Purchase #7	$138.46	4.195%	$144.2684	$144.27	$144.25	$144.30
7 purchase totals =	$947.19		$1,017.3175	$1,017.31	$1,017.30	$1,017.30