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	$150.61	6.595%	$160.5427	$160.54	$160.55	$160.50
Purchase #2	$151.64	10.825%	$168.055	$168.06	$168.05	$168.10
Purchase #3	$7.29	11.240%	$8.1094	$8.11	$8.10	$8.10
Purchase #4	$203.99	12.680%	$229.8559	$229.86	$229.85	$229.90
Purchase #5	$185.60	13.418%	$210.5038	$210.50	$210.50	$210.50
Purchase #6	$35.84	12.620%	$40.363	$40.36	$40.35	$40.40
Purchase #7	$77.92	9.451%	$85.2842	$85.28	$85.30	$85.30
7 purchase totals =	$812.89		$902.7140	$902.71	$902.70	$902.80