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	$76.75	5.455%	$80.9367	$80.94	$80.95	$80.90
Purchase #2	$85.98	4.537%	$89.8809	$89.88	$89.90	$89.90
Purchase #3	$22.32	8.414%	$24.198	$24.20	$24.20	$24.20
Purchase #4	$209.54	7.131%	$224.4823	$224.48	$224.50	$224.50
Purchase #5	$133.60	6.734%	$142.5966	$142.60	$142.60	$142.60
Purchase #6	$76.71	8.631%	$83.3308	$83.33	$83.35	$83.30
Purchase #7	$157.49	10.110%	$173.4122	$173.41	$173.40	$173.40
7 purchase totals =	$762.39		$818.8375	$818.84	$818.90	$818.80