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	$27.72	9.759%	$30.4252	$30.43	$30.45	$30.40
Purchase #2	$199.90	11.568%	$223.0244	$223.02	$223.00	$223.00
Purchase #3	$107.81	4.317%	$112.4642	$112.46	$112.45	$112.50
Purchase #4	$165.36	9.710%	$181.4165	$181.42	$181.40	$181.40
Purchase #5	$248.80	12.170%	$279.079	$279.08	$279.10	$279.10
Purchase #6	$130.46	9.203%	$142.4662	$142.47	$142.45	$142.50
Purchase #7	$40.43	11.471%	$45.0677	$45.07	$45.05	$45.10
7 purchase totals =	$920.48		$1,013.9432	$1,013.95	$1,013.90	$1,014.00