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	$20.70	6.247%	$21.9931	$21.99	$22.00	$22.00
Purchase #2	$136.53	11.567%	$152.3224	$152.32	$152.30	$152.30
Purchase #3	$91.65	13.583%	$104.0988	$104.10	$104.10	$104.10
Purchase #4	$119.26	3.497%	$123.4305	$123.43	$123.45	$123.40
Purchase #5	$247.67	9.841%	$272.0432	$272.04	$272.05	$272.00
Purchase #6	$98.79	12.576%	$111.2138	$111.21	$111.20	$111.20
Purchase #7	$234.79	4.698%	$245.8204	$245.82	$245.80	$245.80
7 purchase totals =	$949.39		$1,030.9222	$1,030.91	$1,030.90	$1,030.80