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	$133.69	11.529%	$149.1031	$149.10	$149.10	$149.10
Purchase #2	$157.76	7.724%	$169.9454	$169.95	$169.95	$169.90
Purchase #3	$24.66	10.848%	$27.3351	$27.34	$27.35	$27.30
Purchase #4	$100.48	9.578%	$110.104	$110.10	$110.10	$110.10
Purchase #5	$74.80	5.486%	$78.9035	$78.90	$78.90	$78.90
Purchase #6	$66.39	7.667%	$71.4801	$71.48	$71.50	$71.50
Purchase #7	$64.89	9.631%	$71.1396	$71.14	$71.15	$71.10
7 purchase totals =	$622.67		$678.0108	$678.01	$678.05	$677.90