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	$178.85	4.216%	$186.3903	$186.39	$186.40	$186.40
Purchase #2	$43.88	11.863%	$49.0855	$49.09	$49.10	$49.10
Purchase #3	$95.66	3.585%	$99.0894	$99.09	$99.10	$99.10
Purchase #4	$128.86	10.307%	$142.1416	$142.14	$142.15	$142.10
Purchase #5	$157.96	9.822%	$173.4748	$173.47	$173.45	$173.50
Purchase #6	$82.56	3.824%	$85.7171	$85.72	$85.70	$85.70
Purchase #7	$211.72	4.827%	$221.9397	$221.94	$221.95	$221.90
7 purchase totals =	$899.49		$957.8384	$957.84	$957.85	$957.80