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	$205.99	6.604%	$219.5936	$219.59	$219.60	$219.60
Purchase #2	$220.45	4.863%	$231.1705	$231.17	$231.15	$231.20
Purchase #3	$41.47	4.682%	$43.4116	$43.41	$43.40	$43.40
Purchase #4	$39.56	7.211%	$42.4127	$42.41	$42.40	$42.40
Purchase #5	$129.71	11.668%	$144.8446	$144.84	$144.85	$144.80
Purchase #6	$9.44	13.200%	$10.6861	$10.69	$10.70	$10.70
Purchase #7	$86.56	3.218%	$89.3455	$89.35	$89.35	$89.30
7 purchase totals =	$733.18		$781.4646	$781.46	$781.45	$781.40