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	$140.47	3.315%	$145.1266	$145.13	$145.15	$145.10
Purchase #2	$22.29	12.560%	$25.0896	$25.09	$25.10	$25.10
Purchase #3	$48.63	12.149%	$54.5381	$54.54	$54.55	$54.50
Purchase #4	$48.27	7.637%	$51.9564	$51.96	$51.95	$52.00
Purchase #5	$75.76	3.311%	$78.2684	$78.27	$78.25	$78.30
Purchase #6	$227.87	12.574%	$256.5224	$256.52	$256.50	$256.50
Purchase #7	$79.76	7.699%	$85.9007	$85.90	$85.90	$85.90
7 purchase totals =	$643.05		$697.4022	$697.41	$697.40	$697.40