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	$34.67	11.359%	$38.6082	$38.61	$38.60	$38.60
Purchase #2	$93.52	8.179%	$101.169	$101.17	$101.15	$101.20
Purchase #3	$20.72	3.320%	$21.4079	$21.41	$21.40	$21.40
Purchase #4	$69.83	12.829%	$78.7885	$78.79	$78.80	$78.80
Purchase #5	$150.50	3.169%	$155.2693	$155.27	$155.25	$155.30
Purchase #6	$183.82	4.281%	$191.6893	$191.69	$191.70	$191.70
Purchase #7	$135.82	8.169%	$146.9151	$146.92	$146.90	$146.90
7 purchase totals =	$688.88		$733.8473	$733.86	$733.80	$733.90