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	$24.74	10.471%	$27.3305	$27.33	$27.35	$27.30
Purchase #2	$15.35	13.844%	$17.4751	$17.48	$17.50	$17.50
Purchase #3	$103.60	8.732%	$112.6464	$112.65	$112.65	$112.60
Purchase #4	$76.89	7.848%	$82.9243	$82.92	$82.90	$82.90
Purchase #5	$65.61	3.213%	$67.718	$67.72	$67.70	$67.70
Purchase #6	$64.34	13.478%	$73.0117	$73.01	$73.00	$73.00
Purchase #7	$125.92	4.153%	$131.1495	$131.15	$131.15	$131.10
7 purchase totals =	$476.45		$512.2555	$512.26	$512.25	$512.10