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	$173.35	4.590%	$181.3068	$181.31	$181.30	$181.30
Purchase #2	$35.99	11.212%	$40.0252	$40.03	$40.05	$40.00
Purchase #3	$181.50	10.705%	$200.9296	$200.93	$200.95	$200.90
Purchase #4	$146.37	13.359%	$165.9236	$165.92	$165.90	$165.90
Purchase #5	$29.95	11.146%	$33.2882	$33.29	$33.30	$33.30
Purchase #6	$191.29	9.187%	$208.8638	$208.86	$208.85	$208.90
Purchase #7	$208.37	12.829%	$235.1018	$235.10	$235.10	$235.10
7 purchase totals =	$966.82		$1,065.4390	$1,065.44	$1,065.45	$1,065.40