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	$182.42	3.285%	$188.4125	$188.41	$188.40	$188.40
Purchase #2	$84.39	7.212%	$90.4762	$90.48	$90.50	$90.50
Purchase #3	$42.30	8.737%	$45.9958	$46.00	$46.00	$46.00
Purchase #4	$173.29	4.856%	$181.705	$181.71	$181.70	$181.70
Purchase #5	$228.91	13.771%	$260.4332	$260.43	$260.45	$260.40
Purchase #6	$156.37	8.800%	$170.1306	$170.13	$170.15	$170.10
Purchase #7	$198.88	10.282%	$219.3288	$219.33	$219.35	$219.30
7 purchase totals =	$1,066.56		$1,156.4821	$1,156.49	$1,156.55	$1,156.40