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	$119.56	3.795%	$124.0973	$124.10	$124.10	$124.10
Purchase #2	$149.76	9.518%	$164.0142	$164.01	$164.00	$164.00
Purchase #3	$74.47	8.604%	$80.8774	$80.88	$80.90	$80.90
Purchase #4	$36.60	10.110%	$40.3003	$40.30	$40.30	$40.30
Purchase #5	$249.64	11.123%	$277.4075	$277.41	$277.40	$277.40
Purchase #6	$175.40	3.140%	$180.9076	$180.91	$180.90	$180.90
Purchase #7	$122.68	7.189%	$131.4995	$131.50	$131.50	$131.50
7 purchase totals =	$928.11		$999.1038	$999.11	$999.10	$999.10