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	$136.48	6.350%	$145.1465	$145.15	$145.15	$145.10
Purchase #2	$173.84	11.432%	$193.7134	$193.71	$193.70	$193.70
Purchase #3	$82.73	8.701%	$89.9283	$89.93	$89.95	$89.90
Purchase #4	$119.62	10.545%	$132.2339	$132.23	$132.25	$132.20
Purchase #5	$212.77	12.244%	$238.8216	$238.82	$238.80	$238.80
Purchase #6	$104.25	9.605%	$114.2632	$114.26	$114.25	$114.30
Purchase #7	$145.32	4.844%	$152.3593	$152.36	$152.35	$152.40
7 purchase totals =	$975.01		$1,066.4662	$1,066.46	$1,066.45	$1,066.40