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	$108.83	3.595%	$112.7424	$112.74	$112.75	$112.70
Purchase #2	$19.79	5.804%	$20.9386	$20.94	$20.95	$20.90
Purchase #3	$132.83	7.463%	$142.7431	$142.74	$142.75	$142.70
Purchase #4	$199.89	10.790%	$221.4581	$221.46	$221.45	$221.50
Purchase #5	$55.76	9.721%	$61.1804	$61.18	$61.20	$61.20
Purchase #6	$158.85	13.404%	$180.1423	$180.14	$180.15	$180.10
Purchase #7	$245.43	5.501%	$258.9311	$258.93	$258.95	$258.90
7 purchase totals =	$921.38		$998.1360	$998.13	$998.20	$998.00