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	$38.78	5.663%	$40.9761	$40.98	$41.00	$41.00
Purchase #2	$18.37	12.840%	$20.7287	$20.73	$20.75	$20.70
Purchase #3	$111.71	9.239%	$122.0309	$122.03	$122.05	$122.00
Purchase #4	$142.52	8.626%	$154.8138	$154.81	$154.80	$154.80
Purchase #5	$40.91	4.353%	$42.6908	$42.69	$42.70	$42.70
Purchase #6	$101.26	12.393%	$113.8092	$113.81	$113.80	$113.80
Purchase #7	$161.89	5.693%	$171.1064	$171.11	$171.10	$171.10
7 purchase totals =	$615.44		$666.1559	$666.16	$666.20	$666.10