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	$47.29	8.131%	$51.1351	$51.14	$51.15	$51.10
Purchase #2	$137.60	9.229%	$150.2991	$150.30	$150.30	$150.30
Purchase #3	$66.43	6.581%	$70.8018	$70.80	$70.80	$70.80
Purchase #4	$156.29	11.526%	$174.304	$174.30	$174.30	$174.30
Purchase #5	$244.57	11.623%	$272.9964	$273.00	$273.00	$273.00
Purchase #6	$21.31	4.632%	$22.2971	$22.30	$22.30	$22.30
Purchase #7	$40.27	3.192%	$41.5554	$41.56	$41.55	$41.60
7 purchase totals =	$713.76		$783.3889	$783.40	$783.40	$783.40