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	$179.58	3.270%	$185.4523	$185.45	$185.45	$185.50
Purchase #2	$85.99	10.554%	$95.0654	$95.07	$95.05	$95.10
Purchase #3	$101.26	10.232%	$111.6209	$111.62	$111.60	$111.60
Purchase #4	$7.67	4.818%	$8.0395	$8.04	$8.05	$8.00
Purchase #5	$139.43	7.853%	$150.3794	$150.38	$150.40	$150.40
Purchase #6	$108.96	4.370%	$113.7216	$113.72	$113.70	$113.70
Purchase #7	$130.42	10.438%	$144.0332	$144.03	$144.05	$144.00
7 purchase totals =	$753.31		$808.3123	$808.31	$808.30	$808.30